Contagious Summary πŸ“– 9 Rules, Tricks & Strategies

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What is Contagious about?

Contagious by Jonah Berger is a great read for anyone into marketing, influence, or the psychology of consumer behavior. It explores what makes people share. In other words: why do certain products, ideas, or content 'go viral'? A lot of research is simplified into 6 key principles: social currency, triggers, emotion, public, practical value, and stories.

Is Contagious worth reading?

Contagious is rated 4.6 on Amazon and 4.0 on Goodreads.

Positive reviews say: Insightful analysis of virality β€” Real-world examples of concepts

Criticism: Narrow focus within marketing β€” Basic for experts


Who is Jonah Berger and why listen to him?

Jonah Berger is a professor at Wharton Business school in Pennsylvania. He is seen as an expert in marketing and social science because he has:

  • Written 3 books,
  • Published over 50 articles in academic journals,
  • Been featured in media like The New York Times and Harvard Business Review.

In this book, Jonah Berger shows us how to succeed with social media using advice that is both practical and most importantly SCIENCE-BASED. In a world of one million self-proclaimed social media “experts,” that’s a breath of fresh air!

It feels like most business teachers today are talking about social media. We all love the idea that other people will promote our business for free on Facebook, Youtube and other platforms. But while it’s true that word of mouth marketing is very powerful, most businesses do not know how to succeed with social media. I’m sure we’ve all had the experience of starting a new social media account and then getting almost no likes or shares aside from some friends. (Hey, at least Aunt Becky liked my post, right?)

Well, if you want people to pay attention to your posts and share them, then you need to understand the PSYCHOLOGY behind what makes people share. And I have some good news! Professor Jonah Berger spent years researching the science of ‘contagiousness’ and in this book he simplified what he learned into six principles. Those principles are:

  1. Social Currency. People share things that make them look good in the eyes of others.
  2. Triggers. You can make remember your product more often and therefore increase word of mouth by designing triggers.
  3. Emotions. People share things that arouse strong feeling in them, both positive and negative feelings.
  4. Public. People naturally imitate what they see others doing, so make sure your product is used in some publicly visible way.
  5. Practical Value. People like to share useful information.
  6. Stories. Information can be embedded into stories because people find stories very easy to remember and share.

So those are the six principles in short. Now in this book summary we’ll explore them in a little more detail. And hopefully, by the time we’re finished, you too will know how to make your ideas spread across the world infecting minds like a virus. (In a good way, of course!)

πŸ•ΆοΈ 1. Social Currency: Give people something to share that makes THEM look good – trendy, smart, or high status

People like to share things about themselves. Scientific studies shown we’re actually wired to find self-sharing pleasurable. Yet what makes us share some things about ourselves and not other things? Jonah Berger says:

We share things that make us look good.

We all want to be seen a certain way by other people. Some might call this superficial and selfish, but it’s also a totally natural and human. People want to be seen as in-demand, attractive, successful, smart, cool and virtuous.

Now, we all know this is true right away, but we usually don’t think about it. Yet of course when we post a new profile photo online, we want it to show us at our best. Beyond photos, we also share activities that make us look good to our peer groups:

  • If you’re a 20 year old guy, then you might post a selfie working out, which makes you look disciplined, driven and on the path to success.
  • If you’re a 40 year old woman, then you might post a photo of a fancy restaurant meal, which makes you look glamorous and somewhat wealthy.
  • If you’re a 60 year old, then you probably can’t figure out how to plug in your smart phone… so this example doesn’t work. (Don’t worry, I’m just kidding. Lot of older people are great at social media now too.)

On the other hand, we don’t want to be seen as unpopular, unattractive or unsuccessful. That’s why almost nobody shares a selfie before going on a 10-hour Netflix marathon or posts a photo of their crumpled McDonald’s burger.

When we talk to others, we’re not only communicating information; we’re also saying something about ourselves. When we rave about a new foreign film or express disappointment with the Thai restaurant around the corner, we’re demonstrating our cultural and culinary knowledge and taste.

This is the first principle and it is called social currency. Things that make us look good are almost like currency, we can use them to buy ourselves a better social reputation. We all know the guy posting a photo of himself riding a Ferrari bought that car for social currency, but the truth is we all do that type of behavior in some subtle ways, even when we are not consciously aware of it.

So next time you’re posting on social media, ask yourself: How can someone in my audience look good by sharing this? If you stop to think about this, then your messages are much more likely to be shared.

For example, Yogi Surprise is a monthly subscription box for yoga lovers. You sign up for $45 per month and receive a monthly box of yoga-related goodies. Now, yoga makes someone look good because they appear to be healthy, attractive and open-minded. So at the time I was writing this summary, on their homepage Yogi Surprise was featuring photos their own users had posted on Instagram expressing their happiness with the product. So their own users were spreading the word about this product because appearing into yoga is positive social currency.

Obviously if you sell something related to yoga, then people will feel much better sharing that than if you sell… adult diapers or whatever. (By the way, I don’t want to denigrate yoga at all, I really love to meditate. Just pointing this out as one example of how we choose what to share.)

We all want to share things about ourselves that make us look good, successful, in-demand, attractive and virtuous. That’s why we post a photo of a nice restaurant meal but not our quick lunch at McDonald’s. Think about how you can give your audience a message to share that makes THEM look great.

✨ 2. Spark Curiosity: Surprise people with novelty and they are more likely to share

Sharing, extraordinary, novel, or entertaining stories or ads makes people seem more extraordinary, novel, and entertaining. It makes them more fun to talk to, more likely to get asked to lunch, and more likely to get invited back for a second date.

One effective way to create social currency is through surprise. We like sharing things that are surprising, new and different. Why? Because it helps US avoid being seen as boring, predictable and stale ourselves!

HOW can we be surprising? It’s not as difficult as you may expect. Jonah sums it up in this great quote:

One way to generate surprise is by breaking a pattern people have come to expect.

Once you understand that surprise is created by breaking an expectation, then you’ll see this happening all over your social media. For example, one video from the TV show “Britain’s Got Talent” received almost 250 million views. Why? It was a video of a 47-year-old woman named Susan Boyle. She doesn’t look pretty, and when she walks on stage everyone expects her voice to match her plain appearance.

Then she opens her mouth and has one of the most beautiful voices you’ve ever heard. Everyone is amazed and she receives a standing ovation. One of the TV hosts even says, “Didn’t expect that, did you?” a few seconds after she starts singing. Take a look at the video for yourself below.

People expect that a beautiful woman will have a beautiful voice. They also expect an unattractive woman to have an unattractive voice. When their expectation is shattered, they feel an incredible surge of emotion. Then they want to share the video with their family and friends.

Even if all you sell is a boring product, there’s probably a way you can make it surprising.

For example, Blendtec is a company that was selling blenders since 1999. But the problem was that nobody really knew the brand. Then one day the founder had a idea to start a Youtube channel called “Will it Blend?” He made many videos where he blended random objects like golf balls, magnets and iPhones.

Well, we all EXPECT someone will put vegetables into a blender and Blendtec broke that expectation. As a result, many of their videos received over 10 million views. Best of all, their sales increased by 700%!

When we are surprised by something, we feel a surge of emotion which makes us more likely to share. Creating surprise is about predicting what people expect to happen, then doing something that breaks that pattern of expectation.

πŸšͺ 3. Cultivate Exclusivity: Making your product harder to get will make it more appealing

If something is difficult to obtain, people assume that it must be worth the effort. If something is unavailable or sold out, people often infer that lots of other people must like it, and so it must be pretty good.

Another form of Social Currency is when a product is scarce, exclusive or difficult to get. If you get something not many other people can get, that implies you have some extra resources, special access or higher status. As a result, we are also more likely to share posts that imply we have obtained something scarce or exclusive.

This doesn’t just apply to luxury products, because part of human nature is we want and value things more when they are hard to get. Jonah Berger looked at a few studies and found that:

People evaluate cookbooks more favourably when they are in limited supply, find cookies tastier when they are scarce, and perceive pantyhose as higher end when it’s less available.

So if you want to instantly make anything more popular, then restrict access to it. During your college years, did you ever stand outside a bar or nightclub in a line for 20 minutes, only to walk in and discover there were few people inside? The owners of these clubs know that if the club looks empty, then nobody will wait in line, but if it looks popular then more and more people will join the line.

Another example is McDonald’s with their McRib sandwich. When they first introduced the sandwich, it was a total failure and they had to take it off the menu. However, many years later some McDonald’s executive decided to try bringing the McRib back as a limited time product. This one change suddenly made the McRib incredibly popular. People knew they couldn’t buy it at any time, so they wanted it more because it was scarce.

When a product is scarce or exclusive, then we naturally value it more. Being able to obtain something exclusive also implies we have some qualities like connections or wealth. This makes it another form of Social Currency, news we are more likely to share.

If you see a puppy while jogging in the park, you might remember that you’ve always wanted to adopt a dog. If you smell Chinese food while walking past the corner noodle shop, you might start thinking about what to order for lunch. Or if you hear an advertisement for Coke, you might remember that you ran out of soda last night. Sights, smells, and sounds can trigger related thoughts and ideas, making them more top of mind.

If you want to make people share your message, product or business during their everyday life, then you need to somehow trigger their memory. You see, if people don’t remember your product when they are with friends, then there is zero chance they will talk about it.

This is actually not as difficult as it might sound. People’s memories are constantly being triggered by things around them. This is the secret reason why so many companies give away free pens, cups and t-shirts. If your dentist gives you a calendar with their phone number on it, then you will be reminded of the dentist in some small way every time you write down an important date. This of course makes you more likely to call their office to set up an appointment.

Kit Kat chocolate bars had become very popular with their advertising campaign based on the slogan “Give me a break…” But around 2007 they were running into some problems and sales were down. Hershey gave Colleen Chorak the job of saving the product brand with a fresh new advertising campaign. Her idea? She knew most people drink coffee a couple times a day, so she wanted to make them think of Kit Kat every time they had a coffee. This campaign was very successful. Berger explains the campaign in the book:

The radio spots featured the candy bar sitting on a counter next to a cup of coffee, or someone grabbing coffee and asking for a Kit Kat. Kit Kat and coffee. Coffee and Kit Kat. The two spots repeatedly paired the two together. The campaign was a hit. By the end of the year it had lifted sales by 8 percent. After twelve months, sales were up by a third. Kit Kat and coffee put Kit Kat back on the map. The then-$300 million brand has since grown to $500 million.

Here’s an opposite example that shows how we can also trigger healthy eating…

A university wanted to help its students eat more vegetables. They decided to test two different slogans for healthy eating to see if one of the slogans would be more effective at improving their eating habits. Here’s how that study went:

One group of students saw the slogan β€œLive the healthy way, eat five fruits and veggies a day.” Another group saw β€œEach and every dining-hall tray needs five fruits and veggies a day.” Both slogans encouraged people to eat fruits and vegetables, but the tray slogan did so using a trigger. The students lived on campus, and many of them ate in dining halls that used trays. So we wanted to see if we could trigger healthy eating behavior by using the dining room tray to remind students of the slogan. (emphasis added)

At the end of the study, the results were clear: The slogan that mentioned the word “tray” made students eat 25% more fruits and vegetables, while the β€œhealthy eating” slogan had no effect. When students were looking at their trays in the cafeteria, they must have remembered the healthy eating message. So the trigger worked.

In the book Pre-Suasion, Professor Robert Cialdini reveals the hidden power our mental associations have over us. He says a study was done in a wine store. They wanted to see if the type of music in the store had any effect on sales. What they found was very surprising. On days when they played classical German music, sales of German wine went up. And on days they played classical French music, sales of French wine went up! By the way, I definitely recommend you also look at our summary of the excellent book Pre-Suasion by Robert Cialdini.

Our memory of a product or brand can be triggered by another thing. For example, Kit Kat chocolate bars made coffee into a trigger for their product and sales increased by $200 million. Brainstorm what everyday object or activity you could turn into a trigger for your product.

😑 5. Emotional Impact: Evoke strong emotions like excitement or anger, and more people will share

The New York Times website publicly shows which of their articles are “Most Emailed” every day. So Jonah Berger wanted to find out why some articles were shared through email and not others. He kept track of these articles for 6 months and at the end did an academic analysis.

He found people were far more likely to share an article through email if it aroused strong emotions in them. It didn’t matter if those were positive emotions like excitement and happiness, or negative emotions like anger and anxiety. It only mattered if the emotions were strong or weak. Articles that only made people feel weak emotions like sadness or contentment were not shared.

If you feel a very strong emotion inside your body, then you are more likely to take action to release that emotion by sharing, commenting or protesting in the streets.

Clever politicians have long known that strong emotions inspire people to action. In the book The True Believer, Eric Hoffer explains how leaders of mass movements like the Nazis and Communists used passionate HATE as a tool to provoke their followers to action. Eric Hoffer said, “Mass movements can spread without belief in a God, but never without belief in a devil.” If you’re interested in the psychology of politics, then check out our summary of that book too: The True Believer by Eric Hoffer.

So if you are writing an article that you want to be shared ask yourself:

  • Will this article make someone’s heart beat faster?
  • Will it make them have butterflies in their stomach?
  • Does it take their breath away?
  • Does it make their blood boil?

People were far more likely to email New York Times articles to their friends when the article aroused strong emotions. Those emotions could be positive like excitement and joy, or negative like anxiety and anger. To release the pressure of the strong emotions, people take action by sharing, commenting or even protesting.

πŸ–ΌοΈ 6. Go For Visuals: Emotionally charged images, not statistics, are more likely to influence people’s behavior

Most teens don’t smoke because they think it’s good for them. And most people who scarf down a Big Mac and large fries and wash it down with a super sized Coke are not oblivious to the health risks. So additional information probably won’t get them to change their behaviour. They need something more. And that is where emotions comes in. Rather than harping on features or facts, we need to focus on feelings, the underlying emotions that motivate people to action.

Humans are not very rational or logical, even though we often pretend to be. We’re mostly driven by our emotions and afterwards our brains create rational explanations to our behavior. So when you’re trying to influence someone, you’ll be far more effective hitting them in the emotions rather than feeding their mind new statistics.

And by the way, “influence” is not always negative. There are many kinds of positive influence and even “positive propaganda.” For example, governments were trying for years to decrease the number of smokers. They had been telling people how bad smoking is with little effect. Then they tried another approach that is more visual and emotional. In many countries, cigarette packs must have disgusting photos printed on them. So every time a smoker goes for a cigarette, they see an image of black lungs or cancer tumours, along with text saying this is the result of smoking for 20 years. This strong emotion of disgust now becomes linked with cigarettes in people’s minds. And now fewer people smoke than ever.

Another example. The New York City health department wanted people to drink less soda. They could have talked about calories and how drinking soda causes obesity, but facts are boring. So they tried a different approach aimed at making people FEEL different about soda. They produced a video ad showing a guy literally drinking fat. It’s a big glass of gooey, sticky, lumpy, gross white fat. This disgusting visual image is hard to forget and for many people Coke will now be a trigger for this image. Take a look at the ad for yourself:

People are naturally more motivated by emotions than logical arguments. For example, governments began printing disgusting images of black lungs on cigarette packs. They found the emotion of disgust tied to those images was more effective than numbers, facts and statistics.

πŸ“£ 7. Promote Public Visibility: Products that are used in public, not private, spread far more quickly

The more others seem to be doing something, the more likely people are to think that thing is right or normal and what they should be doing as well.

If you want your message, product or brand to spread virally, then make it public. This means your current customers should be SEEN using your product in some public and visible way.

People are social animals. We copy what we see others doing. But if nobody can SEE others using your product, then it will not be able to spread socially.

In the book, The Lean Startup, Eric Ries explains 3 growth engines every business can use to grow. One of those is viral spread. He says many tech companies like Apple and Facebook deliberately aim to make their products as viral as possible. For example, most earbuds are black, so Apple made theirs white. This gives users of Apple products a way to publicly show they have an iPhone or iPod in their pocket. This also happened when they added the text “Sent from my iPhone” to every email sent from an iPhone.

By the way, if you’re interested in growing your own startup business, then THE most recommended book for that is The Lean Startup by Eric Ries, for which we have a summaryβ€”go check it out!

Another example. Hotmail was a free email service that struggled for many years. Then one day they added a link to the bottom of all their users emails that said: “Get your free email at” Essentially, each of their users was now advertising Hotmail to all their friends and contacts. Hotmail’s growth exploded, they soon reached 12 million users and were bought by Microsoft for $400 million.

Another example is athlete sponsorships. Why do companies like Nike pay individual athletes millions of dollars to wear their clothing? Because the athletes wear the clothes in public, in front of millions of viewers. Not only is this showing public usage of Nike shoes, but the athlete is also a hero to many young people. The young people want to copy their role model, so they are even more likely to buy the shoes. Nike’s huge growth over the past 20 years is good proof this marketing strategy works.

(And by the way, if you want to hear more about the Nike business success story, then go see our summary of Shoe Dog, a book written by Nike’s founder Phil Knight. It’s very inspiring!)

People are social animals, we naturally copy what we see others doing. So make your product something that is used in a publicly visible way. For example, Hotmail added a short link to the bottom of each of their users emails, and that exploded their growth.

πŸ‘ 8. Practical Value: Content that offers useful information gets more shares

Information that helps people in a practical way is much more likely to be shared. In his New York Times Analysis, Jonah Berger found that USEFUL articles were 30% more likely to hit the Most Emailed list. That makes sense. You want to help your friends. If you see an article that may help them, then you share it.

The famous copywriter Gary Bencivenga said the secret to successful advertising is to “Make your advertising itself valuable.” By this, he meant people have been bombarded so much with advertising that they are mostly blind to it. But if your advertising offers some truly valuable information inside itself, then it will not be ignored. He said, ideally people should find your ad so useful that they cut it out of the newspaper to save it.

In the internet age, this philosophy has transformed into something called content marketing. For example, the company Seattle Coffee Gear sells coffee makers and coffee online. They have a Youtube channel with almost 200 thousand subscribers. The videos educate people how to pick great quality coffee beans, how to brew better coffee, and how to choose the best coffee machine. People who want great coffee will be pulled in by the useful content, some of them will end up becoming customers of Seattle Coffee Gear.

People today are bombarded with clickbait and noisy advertising. To stand out, provide them with information they can use today in some practical way. For example, if you sell coffee makers, then show people how to pick the best coffee beans.

🎭 9. Embed Storytelling: Information wrapped in stories is more engaging and shareable

For thousands of years, before humans could read or write, we shared stories. And these stories were not simply entertainment, they carried important messages inside them. Stories helped information, knowledge, and morals be transmitted down through generations.

Let’s use a very simple example to illustrate this. I’m sure you’ve heard “The 3 Little Pigs” story before right? Three little pigs build three houses. The first two pigs are lazy and quickly build their houses from straw and wood. Then a big bad wolf comes and blows their houses down quite easily. But the third pig had carefully built his house with bricks. When the wolf comes, he huffs and puffs but can’t blow the house down. Of course this is a cute story, but there’s an important lessons hidden within it.

The psychologist Jordan Peterson wrote a textbook called Maps of Meaning that explains this in great detail. He studied religious myths for many years and discovered that underneath the stories were deep truths about existence. What’s even more fascinating is these deep truths are found in many different cultures and religions, when you know how to analyze the myths. For example, every culture has some type of myth where a hero must voluntarily face unknown danger and transform that chaos into order.

Let’s look at a practical example. Subway had a brilliant ad campaign many years ago based on a story. They found a guy called Jared who had lost 245 pound by eating Subway subs. This was a surprising story that people could easily share. Coworkers all over the country could say “Hey did you hear about the Subway guy who lost so much weight eating subs?” So Subway spread his story far and wide, it was a huge success. Let me tell you: a marketing campaign where they directly claimed Subway is healthy would NOT have been nearly as successful.

Humans are designed to share stories. It’s how wisdom was passed down for millions of years before we could read or write. Think of how you could embed your message within a story, like Subway which told the story of Jared losing 245 pounds eating their subs.


Next time you’re about to post on social media, keep those six principles in mind. Now know what makes people share. The next step is to really use this information. That means stopping to think how you can make each individual post a little more shareable, before you click publish.

If you enjoyed this book, then I also recommend Robert Cialdini’s books or “Made to Stick” by Chip and Dan Heath. They also write about psychology and marketing in a fascinating way.

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