Contagious: Book Summary & Review

contagious book cover

Contagious (2013) analyzes the traits and characteristics that viral products, ads, and ideas all have in common.
It’s 6 characteristics they all share, and if you want to go viral, you better incorporate them in your marketing.

Exec Summary

  • Virality is not the product of pure chance
  • You can increase the odds of going viral by incorporating some of the 6 principles

Contagious Book Summary

About The Author: Jonah Berger holds a Ph.D. in marketing and is currently a professor at the Wharton School. He is considered an expert on word of mouth, social influence, and viral marketing.

The $100 Dollar Cheesesteak Gone Viral

Berger starts with the example of  Howard Wein.

Wein was not selling just another cheesesteak, but a conversation piece. He did it by using great ingredients and asking for an exorbitant price: a hundred dollars.

It went viral.

Great Products Go Viral

Jonah Berger beings by saying that one of the elements of virality is simply having a great product.

Some ideas catch on for simply being better than the alternatives.

Attractive pricing is another obvious why products and ideas spread.
Advertising also helps, Jonah Berger says that word of mouth is more effective than advertising because it’s more persuasive and more targeted.

Jonah Berger goes after the idea that you have to hit the opinion leaders to make your message spread.
He says though that the message in itself is more important than the messenger.

What is then the secret to making our messages contagious?

Jonah Berger says that it’s six principles:

  1. Social currency (people looking cool for sharing),
  2. Triggers (reminding people about our product)
  3. Emotions (when we care we share)
  4. Public (can people see we are using the product?)
  5. Practical Value (is it useful?)
  6. Stories (what narrative can we latch onto our idea?).

It’s important to notice that Jonah Berger says that principles are not like ingredients.
They must not be deployed in a certain fashion, and they are not even all needed at the same time.


Jonah Berger says there are three ways to use social currency:

  1. Find something unique
  2. Use game mechanics
  3. Make people feel like insiders

More remarkable products are talked about twice compared to less remarkable ones.

Game mechanics are levels and badges that make us want more.
Berger says that it works internally as we all love achievement, but also because we want to do better than others. Icons can be used, or badges (fourth square).

Making people feel like insiders works because If something is supposed to be secret or limited access people love to share it.
It makes them look cool for sharing something reserved. They were one of the first in the know, and now they’re sharing it with you.

People shared the video of a blender smashing marbles because it was interesting and unexpected.
And sharing something that others will find interesting will give us social points.

Here’s the video the author refers to:


People talk about more cheerios than Disney World.

How’s that possible with all the excitement and uniqueness that Disney World commands?

The author says it’s because of triggers.
People rarely go to Disney World and few things remind them of it.
Cheerios are seen often at the supermarket and breakfast every day reminds people of Cheerios.

Jonah Berger says that interesting products receive more immediate word of mouth than boring ones, but interesting per se doesn’t sustain word of mouth over time. Triggers do. When we see the same triggers over and over, the product comes back to our minds over and over.

The author says that Mars bars saw a big uptick in sales when NASA launched an expedition to, guess where?

KitKat was seeing a constant slump in sales that seemed hard to stop.
It was reversed when an advertising campaign linked KitKat to coffee so that people would use the coffee trigger to eat a KitKat bar.


There are two types of emotions that lead people to share (or not share):

  • Arousing emotions
  • non-arousing emotions

Emotions that make us share are arousing emotions like anger, awe, anxiety, or excitement.
Sadness and contentment decrease arousal, slow us down and make us relax, leading us to share less.

Very interestingly, Jonah Berger says that when we are in aroused states we tend to share more than we’d normally want.
So if we are on a plane with turbulences, we might tell the person sitting next to us more than we would normally like.

The author says that focusing on feelings is likely to increase sharing and even seemingly dull products can find a way (for example: google search with the story of a couple told through their search queries).


Jonah Berger presents very few interesting cases on how what’s public influences us even when in private most people would think otherwise.

For example, many college students don’t enjoy drinking but drink anyway because externally everybody is drinking and all others who don’t enjoy drinking are actually keeping it private.

Similarly, when a presentation has finished and the presenter asks if there are any questions nobody asks anything, because while nobody else has probably understood, the public and visible tell us that we are probably the only ones who didn’t get it.

The author provides a few examples of a few products that effectively used the observability principle.
Hotmail for example, put in the signature the link to sign up for the free service (it was the first free service).
Apple white iPod headphones were a big help in spreading it.

The example of the anti-drug “say no” campaign was also extremely interesting.
Jonah Berger says that the campaign actually increased the likelihood people would try drugs because it brought drug use into the public observable territory.
The ads basically said that drugs are bad but also, crucially, that other people are doing it.

The example of the music industry was simply a big laugh for me.
When the ads said that only 37% of music was being paid for, the author implies the message was counterproductive.
It basically said that everyone was not paying, that it was OK not to pay, and that those paying must have been idiots (similar example for wood in the park).

If something is built to show, it’s built to grow


Jonah Berger says we share useful information because we want to help and if we can help it reflects well on us.

Putting a product on sale, even when the price stays the same, increases demand.

The author says that depending on the price of the product it can be better to list the discount as in percentage or as an amount.
The author says that for products above 100, it’s better to highlight the amount and for products worth less than 100 it’s better to state the percentage.


Jonah Berger says that we don’t think in terms of information but in terms of narrative.

It’s important that the story is relevant to the product, or the product has to be a key part of the story.

contagious book cover

Contagious Book Review

“Contagious” is easy to read, insightful, and highly applicable.

It makes a great pair with a few more books on marketing and influencing such as Make to Stick“, “The Tipping Point“, “Triggers“, “Brandwashed and “Influence, the big classic by Cialdini.

Of course, as the author himself says, “Contagious” is not a recipe that you can apply and be guaranteed success.
I’m afraid that virality is, in good part, the product of pure randomness.

But that doesn’t mean you can’t somewhat increase the odds with some good knowledge, research, and creativity.

Highly recommended, and you can get it here on Amazon.

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