Contagious by Jonah Berger [Book Summary & PDF]

In Contagious, Berger reveals the secret science behind word-of-mouth and social transmission. We’ll discover how six basic principles drive all sorts of things to go viral, providing a set of specific, actionable techniques to craft contagious content.





Who is this book for?

Whether you're a manager at a big company, a small business owner trying to boost awareness, a politician running for office, or a health official trying to get the word out, Contagious will show you how to make your product or idea catch on.

About the author

Jonah Berger is a marketing professor at the Wharton School at the University of Pennsylvania and bestselling author of Contagious and Invisible Influence. Dr. Berger has spent over 15 years studying how social influence works and how it drives products and ideas to catch on. He’s published dozens of articles in top-tier academic journals, consulted for a variety of Fortune 500 companies, and popular outlets like the New York Times and Harvard Business Review often cover his work.

In this summary

In Contagious, Berger reveals the secret science behind word-of-mouth and social transmission. We’ll discover how six basic principles drive all sorts of things to go viral, providing a set of specific, actionable techniques to craft contagious content. Let’s explore them!



Virality isn’t born; it’s made. Some people claim that products become popular because they are just plain better, cheaper, and better advertised

But although these factors contribute to products, ideas, and content being successful, they don’t explain the whole story. The other part of the equation is social influence and word of mouth. People love to share stories, news, and information with those around them. Actually, word of mouth is the primary factor behind 20% to 50% of all purchasing decisions.

The author of Contagious spent years researching and found that, regardless of how plain or boring a product or idea may seem, there are ways to make it contagious:

Social Currency – Triggers – Emotion – Public – Practical Value – Stories

Follow the aforementioned 6 key STEPPS, and you can harness social influence and word of mouth to get any product or idea to catch on.

Let’s explore them!


“We share things that make us look good”

Most people would rather look smart than dumb, rich than poor, and cool than boring. Makes sense, right?

Just like the clothes we wear and the cars we drive, what we talk about influences how others see us. It’s called social currency.

We use money to buy products or services. Likewise, we use social currency to achieve desired positive impressions among our families, friends, colleagues, and society at large.

Knowing about cool things – like a blender that can tear through an iPhone – makes people seem sharp and in-the-know.

In other words, to get people talking about our products, ideas, or content, we need to craft messages that help them achieve these desired impressions.

There are 3 ways to mint social currency.

  1. Find Inner Remarkability

Remarkable things are defined as unusual, extraordinary, or worthy of notice or attention.

Something can be remarkable because it is novel, surprising, extreme, or just plain interesting. It breaks a pattern people have come to expect. But the most important aspect of remarkable things is that they are worthy of mention.

Find the inner remarkability in any product or idea by thinking about what makes it stand out.

  1. Leverage Game Mechanics

Game mechanics are the elements of a game, application, or program that make them fun and compelling. These elements tell players where they stand in the game and how well they are doing.

Good game mechanics keep people engaged, motivated, and always wanting more, because we all enjoy achieving things (internal motivation) and social comparison (interpersonal motivation).

This is how game mechanics boosts word of mouth. People are talking because they want to show off their achievements, but along the way they talk about the brands or domains where they achieved. Loyalty cards, badges, awards, and collecting points or miles are examples of gamification.

  1. Make People Feel Like Insiders

Both scarcity and exclusivity make customers feel like insiders:

  • Scarce things are less available because of high demand, limited production, or restrictions on the time or place you can acquire them.
  • Exclusive things are accessible only to people who meet particular criteria, know certain information or are connected to people who do.

Scarcity and exclusivity boost word of mouth by making people feel like insiders. If people get something not everyone else has, it makes them feel special, unique, high status. Having insider knowledge is social currency.

Now, Ask Yourself…

  • Does talking about your product or idea make people look good?
  • Can you find the inner remarkability?
  • …Leverage game mechanics?
  • …Make people feel like insiders?


“Top of mind, tip of tongue”

People talk about Cheerios more than Disney World. The reason? Triggers.

Triggers are stimuli that prompt people to think about related things. Peanut butter reminds us of jelly and the word dog reminds us of the word cat.

People often talk about whatever comes to mind, so the more often people think about a product or idea, the more it will be talked about.

Sights, smells, and sounds can trigger related thoughts and ideas, making them more top of mind. Top of mind leads to tip of tongue.

Triggers is the reason behind negative word of mouth having positive effects: a bad review or negative word of mouth can increase sales, if it informs or reminds people that a product or idea exists.

How do we remind people to talk about our products and ideas?

  1. Design products and ideas that are frequently triggered by the environment. Take hot dogs. Barbecues, summertime, baseball games, and even wiener dogs (dachshunds) make up their natural habitat.
  2. Create new triggers by linking our products and ideas to prevalent cues in that environment. Kit Kat wouldn’t normally be associated with coffee, but through repeated pairing & advertising, they were able to link the two.

A strong trigger can actually be much more effective than a catchy slogan. Competitors can even be used as a trigger, by making a rival’s message act as a trigger for your own.

Now, Ask Yourself…

  • What is the natural habitat of your products or ideas?
  • What cues make people think about your products or ideas?
  • How can you grow the habitat and make them come to mind more often?


“When we care, we share”

How can we craft messages and ideas that make people feel something?Blending an iPhone is surprising. A potential tax hike is infuriating. A dog that sings metal is hilarious.

Naturally contagious content usually evokes some sort of emotion. Emotional things often get shared. Why? Sharing emotions also helps us connect. Feeling the same way with someone else helps deepen our social connection, highlighting our similarities and reminding us how much we have in common.

Rather than harping on function, then, we need to focus on feelings. However, not all emotions do the work; some emotions increase sharing, while others actually decrease it.

In general, positive articles are more likely to be highly shared than negative ones. For example:

  • Awe is the experience of confronting something greater than yourself. Awe-inspiring articles are 30% more likely to be highly shared.
  • Sadness, on the other side, has the opposite effect. Sadder articles are 16% less likely to get shared.

Surprisingly, though, articles that evoke negative emotions, such as anger or anxiety, are also more likely to get broadly shared. Why is that? Because some emotions, like anger and anxiety, are high-arousal. Arousal is a state of activation and readiness for action. The heart beats faster and blood pressure rises.

“When aroused, we do things. ”

When we’re angry we yell at customer service representatives. When we’re anxious we check and recheck things.

Positive emotions also generate arousal. Take excitement. When we feel excited we want to do something rather than sit still. The same is true for awe. When inspired by awe we can’t help wanting to tell people what happened.

Other emotions, such as sadness or contentment, have the opposite effect: they stifle action. When trying to use emotions to drive sharing, remember to select high-arousal emotions that drive people to action. Excite people or inspire them by showing them how they can make a difference. Make people mad, not sad.

High Arousal – Low Arousal – Positive – Awe – Excitement – Amusement (Humour) – Contentment – Negative – Anger – Anxiety – Sadness

Now, Ask Yourself…

  • Does talking about your product or idea generate emotion?
  • How can you kindle the fire with high-arousal emotions?


“Built to show, built to grow”

The famous phrase “Monkey see, monkey do” captures more than just the human tendency to imitate. It also tells us that it’s hard to copy something you can’t see.

Making things more observable makes them easier to imitate, which makes them more likely to become popular.

“People imitate, in part, because others’ choices provide information,” says the author. If other people are doing something, we assume it must be a good idea, because they probably know something we don’t.

Psychologists call this idea social proof. Observability also spurs purchase and action.

So, do you want your idea to catch on? Make sure people don’t just ‘think’ it’s great, but they also do something publicly about it.

For example, people who sport a moustache effectively for the 30 days of November become walking, talking billboards against prostate cancer, testicular cancer, and mental health for me. The Movember Foundation succeeded because they figured out how to make the private public. They figured out how to take support for an abstract cause – something not typically observable – and make it something that everyone can see.

In short, we need to make our products and ideas more public, taking what was once an unobservable thought or behaviour and transforming it into a more observable one.

We need to design products and initiatives that advertise themselves. Hotmail, iPhone, and BlackBerry emails are all examples of products that advertise themselves (e.g. ‘Sent from my iPhone’). Every time people use the product or service they also transmit social proof or passive approval because usage is observable.

Shapes, sounds, and a host of other distinctive characteristics can also help products advertise themselves.

Designing products that advertise themselves is a particularly powerful strategy for small companies or organisations that don’t have a lot of resources.

“It’s like advertising without an advertising budget.”

Now, Ask Yourself…

  • Does your product or idea advertise itself?
  • Can people see when others are using it?
  • If not, how can you make the private public?
  • Can you create behavioural residue that sticks around even after people use it?
“It’s like advertising without an advertising budget.”Click To Tweet


“News you can use”

When writer and editor William F. Buckley Jr. was asked which single book he would take with him to a desert island, his reply was straightforward:

“A book on shipbuilding.”

Useful things are important. If Social Currency is about information senders and how sharing makes them look, Practical Value is mostly about the information receiver.

Sharing something useful with others is a quick and easy way to help them out. People like to help others, so if we can show them how our products or ideas will save time, improve health, or save money, they’ll spread the word.

But given how inundated people are with information, we need to make our message stand out.

The Psychology of Deals

We need to understand what makes something seem like a particularly good deal. People evaluate deals relative to a comparison standard, or “reference point.”

A grill seems like a better deal when it is marked down from $350 to $250 rather than when it is discounted from $255 to $240, even though it is the same grill. Setting a higher reference point makes the first deal seem better, even though the price is higher overall.

Strangely, using the word “sale” beside a price increases sales, even if the price itself stays the same!

Highlighting Incredible Value

Restricting availability through scarcity and exclusivity makes things seem more valuable.

Offers that are available for only a limited time seem more appealing because of scarcity. Likewise, the fact that a deal won’t be around forever makes people feel that it must be a really good one. Even restricting who has access can make a promotional offer seem better.

Beyond Money

We need to package our knowledge and expertise so that people can easily pass it on.

For example, sending out a rambling four-page email with 25 advice links about 15 different topics is not useful. Instead, send out a short, one-page note, with a key header article and 3 or 4 main links below it. It’s easy to see what the main points are, and if you want to find out more, you can simply click on the links.

Now, Ask Yourself…

  • Does talking about your product or idea help people help others?
  • How can you highlight incredible value, packaging your knowledge and expertise into useful information others will want to disseminate?


“Information travels under the guise of idle chatter”

What broader narrative can we wrap our idea in? This question is important, because people don’t just share information; they tell stories.

Just like the epic tale of the Trojan Horse, stories are vessels that carry things, such as information, morals, and lessons. Information travels under the guise of what seems like idle chatter.

Today, even with thousands of entertainment options, our tendency to tell stories remains. We get together around our proverbial campfires – now water coolers, meetups, or girls’/guys’ night out – and tell stories.

Stories are an important source of cultural learning that help us make sense of the world. They save time and hassle and give people the information they need in a way that’s easy to remember.

We need to build our own Trojan horses, embedding our products and ideas in stories that people want to tell. In essence, stories provide a sort of psychological cover that allows people to talk about a product or idea, without seeming like an advertisement.

Sure, you can make your narrative funny, surprising, or entertaining. But if people don’t connect the content back to you, it’s not going to help you very much. Even if it goes viral.

Virality is most valuable when the brand or product benefit is integral to the story. We need to make our message so integral to the narrative, that people can’t tell the story without it.

When you build a Social Currency–laden, Triggered, Emotional, Public, Practically Valuable Story, don’t forget to hide your message inside it. Make sure your desired content, product, or idea is so embedded into the plot, that people can’t tell the story without it.

Now, Ask Yourself…

  • What is your Trojan Horse story?
  • Is your product or idea embedded in a broader narrative that people want to share?
  • Is the story not only viral, but also valuable?


Key takeaways

  • Virality isn’t born, it’s made – just follow the 6 key STEPPS.
  • Social Currency: People share things that help them look good, smart, and cool to their family, friends, and society.
  • Triggers: People talk about whatever is on top of mind; the more often people think about a product or idea, the more it will be talked about.
  • Emotion: Contagious content evokes high-arousing emotions (awe, surprise, anger, anxiety etc.), which make things get highly shared.
  • Public: Making things more observable makes them easier to imitate, which makes them more likely to become popular.
  • Practical Value: Sharing something useful is a quick and easy way to help others out.
  • Stories: Embed our products & ideas in stories that people want to tell.

Further reading

Inspired: How to Create Products Customers Love by Marty Cagan is a well-written book detailing the process of creating a product, whether that be internet based or physical. Cagan starts from the beginning with the key roles of team members, takes you through the development process and finishes with marketing and selling your product.

Guidelines is my eBook that summarises the main lessons from 33 of the best-selling self-help books in one place. It is the ultimate book summary; Available as a 80-page ebook and 115-minute audio book. Guidelines lists 31 rules (or guidelines) that you should follow to improve your productivity, become a better leader, do better in business, improve your health, succeed in life and become a happier person.

Action steps

  1. Start crafting content that could become contagious, answering the questions at the end of each chapter and testing it with an audience.
  2. Go to to get more resources on the subject.
  3. Read the full book to study the case studies mentioned, download on Amazon.

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