# Contagious Why Things Catch On

> Knowledge base from "Contagious: Why Things Catch On" by Jonah Berger. Use when applying Berger's STEPPS framework for word of mouth, virality, social currency, triggers, emotion, social proof, practical value, and storytelling, studying the book, or referencing its concepts.

- Skill: `lionelndong/contagious-why-things-catch-on` (Agent Skill, multi-file: 12 files)
- Install (CLI): `npx skillmds add lionelndong/contagious-why-things-catch-on`
- Raw SKILL.md: https://api.skillmd.com/api/skills/lionelndong/contagious-why-things-catch-on/raw
- Safety review: pending (external: skill-scanner PASS, skillspector CAUTION)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Docs & Writing
- Author: lionelndong (https://skillmd.com/u/lionelndong)
- Updated: 2026-08-19
- Page: https://skillmd.com/skills/lionelndong/contagious-why-things-catch-on

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# 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.

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## 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.

| | Principle | Mantra | Core move |
|---|---|---|---|
| **S** | Social Currency | *We share things that make us look good* | Make talking about it make people look good |
| **T** | Triggers | *Top of mind, tip of tongue* | Link it to frequent environmental cues |
| **E** | Emotion | *When we care, we share* | Evoke high-arousal emotion |
| **P** | Public | *Built to show, built to grow* | Make it observable; leave residue |
| **P** | Practical Value | *News you can use* | Package genuinely useful info |
| **S** | Stories | *Info travels under idle chatter* | Wrap it in a Trojan-Horse narrative |

### 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).

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## Chapter Index

| # | Title | Key Frameworks |
|---|-------|----------------|
| [ch00](chapters/ch00-introduction.md) | Introduction: Why Things Catch On | STEPPS, message-over-messenger, virality is made, 7% rule |
| [ch01](chapters/ch01-social-currency.md) | Social Currency | inner remarkability, game mechanics, scarcity & exclusivity, social incentives |
| [ch02](chapters/ch02-triggers.md) | Triggers | triggers, immediate vs. ongoing WOM, grow the habitat, poison parasite |
| [ch03](chapters/ch03-emotion.md) | Emotion | arousal framework, awe, focus on feelings, Three Whys, "mad not sad" |
| [ch04](chapters/ch04-public.md) | Public | observability, social proof, make the private public, behavioral residue |
| [ch05](chapters/ch05-practical-value.md) | Practical Value | prospect theory, reference points, Rule of 100, packaging value |
| [ch06](chapters/ch06-stories.md) | Stories | Trojan Horse, valuable virality, proof by analogy, critical vs. extraneous |
| [ch07](chapters/ch07-epilogue.md) | Epilogue | STEPPS as a system, forest-fire model, universality |

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

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## 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.