Contagious Why Things Catch On

Contagious: Why Things Catch On

Author: Jonah Berger (Wharton) | Words: ~70K | Chapters: Intro + 6 (STEPPS) + Epilogue | Generated: 2026-06-29

How to Use This Skill

• Without arguments — load the core frameworks below for reference.
• With a topic — ask about social currency, triggers, emotion, social proof, practical value, stories, rule of 100, etc.; I read the relevant chapter.
• With a chapter — ask for ch03; I load that chapter file.
• Browse — ask "what chapters do you have?" for the full index.

When a topic isn't fully covered below, I read the relevant chapter file before answering.

Core Frameworks & Mental Models

STEPPS — the six principles of contagiousness

The book's spine. Six ingredients that make products, ideas, and behaviors spread by word of mouth. You don't need all six — treat them like salad toppings, not a strict recipe.

Foundational theses

• Virality is made, not born. Any product/idea — even a "boring" blender — can be engineered to be contagious (Will It Blend?).
• Message over messenger. Focus on what makes the idea worth sharing, not on finding a few "influentials." Social epidemics are forest fires carried by thousands of ordinary people, not big sparks (Duncan Watts).
• ~7% of word of mouth is online. Offline talk is more prevalent and often more impactful. Social media is a technology, not a strategy.

Social Currency (Ch 1)

We share to look good. Three ways to mint it: (1) inner remarkability (find what's novel/surprising/pattern-breaking); (2) game mechanics (quantify performance, give legible, show-off-able status — miles, badges, tiers); (3) make people feel like insiders via scarcity (limited amount) and exclusivity (limited access, incl. by knowledge). Use social, not monetary, incentives — paying crowds out intrinsic sharing.

Triggers (Ch 2)

Cues that make a product top of mind → tip of tongue. Interest drives immediate WOM; triggers drive ongoing WOM. Consider the context: pick frequent cues placed near the desired behavior (Kit Kat↔coffee; "Man Drinks Fat" at point of soda). Frequency must be balanced with strength — a cue tied to everything triggers nothing. Grow the habitat by pairing your product with a prevalent stimulus.

Emotion (Ch 3)

Arousal, not positivity, drives sharing. High-arousal emotions share (awe, excitement, humor, anger, anxiety, disgust); low-arousal ones suppress (sadness, contentment). Focus on feelings, not features; use the Three Whys to find the emotional core; make them mad, not sad. Even physical arousal (running in place) boosts sharing.

Public (Ch 4)

"Monkey see, monkey do" — people imitate only what they can see. Use social proof (a line means good food). Make the private public (Movember moustaches; "I Voted" stickers), design products that advertise themselves (white iPod earbuds; "Sent from my iPhone"), and create behavioral residue — durable visible traces (Livestrong wristbands). To stop a behavior, do the inverse: make the public private and stress the positive norm (anti-drug ads backfire by signaling "everyone does it").

Practical Value (Ch 5)

News you can use — people share useful info to help others. Value is judged relative to a reference point (prospect theory), with diminishing sensitivity. Use the Rule of 100: % off under $100, $ off over $100. Restrict availability (time/quantity/access) to raise perceived value. Package expertise into short, scannable units; target narrow audiences; make value visible. Verify before sharing — false "useful" info spreads fast.

Stories (Ch 6)

People think in narratives. Build a Trojan Horse — a story people want to tell that carries your message inside. Aim for valuable virality: make the brand integral, so the story can't be told without it (Panda cheese; Will It Blend?). Virality without integration wastes the spread ("fool in the pool"; Evian roller babies). Stories persuade via transportation and proof by analogy; plan for retelling (critical details survive, extraneous ones drop out).

Chapter Index

Topic Index

• Arousal → ch03
• Awe → ch03
• Behavioral residue → ch04
• Deals / discounts / pricing → ch05
• Emotion → ch03
• Exclusivity → ch01
• Forest-fire model / influentials → ch00, ch07
• Game mechanics → ch01
• Grow the habitat → ch02
• Inner remarkability → ch01
• Make the private public → ch04
• Observability → ch04
• Packaging useful info → ch05
• Poison parasite → ch02
• Practical Value → ch05
• Proof by analogy → ch06
• Prospect theory / reference points / diminishing sensitivity → ch05
• Public / Public visibility → ch04
• Rule of 100 → ch05
• Scarcity → ch01, ch05
• Social currency → ch01
• Social proof → ch04
• STEPPS → ch00, ch07
• Stories / Trojan Horse → ch06
• Three Whys → ch03
• Triggers → ch02
• Valuable virality → ch06
• Word of mouth (immediate vs. ongoing) → ch00, ch02
• 7% (online vs. offline WOM) → ch00

Supporting Files

• glossary.md — all key terms with definitions
• patterns.md — every technique, organized by STEPP
• cheatsheet.md — the six-STEPPS checklist, arousal table, Rule of 100, decision rules, tells & smells

Scope & Limits

This skill covers the book content only. For applying STEPPS to a specific product, campaign, or channel, combine it with your own context and data. For topics beyond this book, check related skills or ask the agent directly.