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Contagious: Why Things Catch On
Jonah Berger · 2013
In a sentence
Products, ideas, and behaviors catch on not because of luck or special people, but because they embody six shareable qualities captured in the STEPPS framework.
Why do some products, ideas, and behaviors become popular while most fail? Wharton marketing professor Jonah Berger argues that virality is made, not born, and that the secret lies in understanding the psychology of why people talk and share. Drawing on years of rigorous research analyzing thousands of New York Times articles, baby names, car purchases, and word-of-mouth campaigns, Berger distills six principles—Social Currency, Triggers, Emotion, Public, Practical Value, and Stories (STEPPS)—that make content contagious. With memorable examples from a hundred-dollar cheesesteak to blending iPhones to viral Google ads, Contagious gives marketers, entrepreneurs, nonprofits, and anyone with a message a practical, science-based toolkit for engineering word of mouth and making ideas spread.
The four lenses
- Science
- Statistics
- Systems
- Strategy
The model
A framework explaining how six design levers (Social Currency, Triggers, Emotion, Public, Practical Value, Stories) influence psychological and behavioral states that drive social transmission and the popularity of products, ideas, and behaviors.
Social Currencydesign lever
The degree to which talking about a product or idea makes a person look good, smart, cool, or in-the-know to others, achieved through inner remarkability, game mechanics, and feeling like an insider.
Triggersdesign lever
Stimuli in the environment that remind people of a related product or idea, keeping it top of mind so it is more likely to be talked about; depends on the frequency and strength of the cue and its link to the desired behavior.
Emotiondesign lever
The extent to which a product, idea, or message evokes feelings in people, particularly high-arousal emotions like awe, excitement, amusement, anger, or anxiety, as opposed to low-arousal emotions like sadness or contentment.
Physiological Arousalpsychological state
A state of bodily activation and readiness for action characterized by increased heart rate and blood pressure, which mediates the relationship between emotion (or physical activity) and the drive to share information with others.
Public Observabilitydesign lever
The degree to which a product, behavior, or idea can be seen by others when used or adopted, enabling social proof and imitation; encompasses self-advertising design and behavioral residue that persists after use.
Practical Valuedesign lever
The usefulness of information for helping others save time, save money, improve health, or have better experiences, made more shareable through remarkable deals and packaged expertise.
Storiesdesign lever
Narratives that carry information, lessons, or brand messages embedded within them, acting as Trojan horses that people pass along while transmitting the embedded content under the guise of idle chatter.
Valuable Viralitycontextual condition
The degree to which the brand or desired message is integral to the narrative such that people cannot tell the story without mentioning it, ensuring that sharing benefits the sponsoring product or organization rather than just spreading the content.
Social Transmission (Word of Mouth)behavioral pattern
The act of people talking about, sharing, forwarding, or imitating a product, idea, or behavior with others through word of mouth and social influence, both online and offline.
Popularity / Catching Onoutcome metric
The outcome in which a product, idea, or behavior diffuses through a population, becoming widely adopted, talked about, purchased, or imitated, constituting a social epidemic.
How they connect
- social currency → predicts social transmission
- triggers → predicts social transmission
- emotion → predicts physiological arousal
- physiological arousal → predicts social transmission
- emotion → mediates social transmission
- public observability → predicts social transmission
- public observability → predicts popularity catching on
- practical value → predicts social transmission
- stories → predicts social transmission
- valuable virality → moderates stories
- social transmission → predicts popularity catching on
- social currency → influences popularity catching on
A candidate measure
Contagious: Why Things Catch On — derived measurement candidates
Social Currency
Remarkability ratings; Frequency of brand mentions; Exclusivity/scarcity scores
self-report suitability: medium
Triggers
Cue frequency counts; Time-series mention spikes; Co-occurrence of cue and mention
self-report suitability: low
Emotion
Rater-coded emotion scores; Textual emotion-word counts; Self-reported emotional intensity
self-report suitability: high
Physiological Arousal
Heart rate and blood pressure measures; Manipulation checks for arousal; Skin conductance
self-report suitability: medium
Public Observability
Visibility coding of behavior; Presence of physical residue; Branding prominence
self-report suitability: medium
Practical Value
Usefulness ratings; Deal attractiveness scores; Forward/share counts of useful content
self-report suitability: high
Stories
Narrative structure coding; Retelling rates; Embedded message presence
self-report suitability: medium
Valuable Virality
Brand recall after exposure; Brand mention rate in retellings
self-report suitability: low
Social Transmission (Word of Mouth)
Word-of-mouth episode counts; Share/forward counts; Most E-Mailed list appearance
self-report suitability: medium
Popularity / Catching On
Sales growth percentage; View/user counts; Market penetration rates
self-report suitability: none
The story
The reader A marketer, entrepreneur, nonprofit leader, politician, or anyone who wants their product, idea, or behavior to spread and catch on.
External problem
Their product or idea isn't getting talked about, shared, or adopted despite its merits.
Internal problem
They feel frustrated and powerless, believing virality is random luck or reserved for those with big budgets or famous connections.
Philosophical problem
It's wrong that great ideas should fail simply because no one understands the science of why people share.
The plan
- Find the inner remarkability and craft social currency around your idea.
- Identify and create triggers that keep your idea top of mind.
- Evoke high-arousal emotions that make people want to share.
- Make your product or behavior more publicly observable.
- Highlight the practical value so people pass it on to help others.
- Wrap your message in a story that people can't tell without mentioning you.
Success
- Your product or idea spreads through word of mouth without a huge advertising budget.
- People talk about, share, and imitate your message naturally.
- Your business, cause, or initiative catches on and flourishes against the odds.
At stake
- Your product or idea goes unmentioned and fails to gain traction.
- You waste money on advertising that is less effective than free word of mouth.
- Your message gets lost in the clutter and never spreads.
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