Berger identifies six STEPPS that make content and products more likely to be shared: Social currency, Triggers, Emotion, Public, Practical value, and Stories. Grounded in academic research rather than anecdote, it explains the mechanics behind word-of-mouth rather than just celebrating examples of it.
Word of mouth has mechanics, not just luck
Berger's contribution is methodological before it is conceptual. The standard viral-marketing book collects things that spread, finds a shared feature and calls it a cause. Berger, a marketing professor at Wharton, went the other way: he ran controlled experiments and large-scale content analysis — most famously a study with Katherine Milkman analysing thousands of New York Times articles to see which characteristics predicted making the most-emailed list — and built the framework out of what actually correlated. The six factors he lands on, packaged as STEPPS, are Social currency, Triggers, Emotion, Public, Practical value and Stories.
The underlying argument is that word of mouth is not the residue of a big advertising budget but a substitute for one, and that it beats advertising on two counts: it is more persuasive, because it comes from someone with nothing to gain, and it is better targeted, because people only pass things to those they think will care. His other early point is a corrective to the industry's obsession with influencers. Most word of mouth is offline, ordinary and unglamorous, coming from people with no particular reach — which means the sensible investment is in making the thing itself worth talking about, not in finding special people to talk about it.
Social currency and triggers
Social currency is the finding that people share what makes them look good — in the know, interesting, generous, ahead of the curve. So the practical question isn't only 'is this useful', it's 'does passing this on make the sharer look better to the person receiving it'. Berger's examples run from a New York bar hidden behind a phone box in a hot dog shop, where the whole product is the pleasure of being the person who knows about it, to game mechanics and status tiers that manufacture something to mention, to what he calls inner remarkability — the Blendtec blender videos being the obvious case, where an unremarkable product was made remarkable by doing something genuinely surprising with it.
Triggers is the chapter most people underrate and the one that does the most work commercially. The finding is that top-of-mind isn't enough on its own; the thing has to be linked to a cue people already encounter frequently, so the association fires without you paying for it. Berger's illustration is the Kit Kat campaign that deliberately tied the bar to coffee — a thing people encounter every day, and one they were already doing when they ate it. He contrasts high-attention campaigns that produce a spike and then nothing with lower-key ones that attach themselves to a recurring moment and keep working. His cautionary case is a public health campaign whose repeated anti-drug messaging appears to have functioned as a trigger for thinking about drugs rather than avoiding them.
Emotion, public visibility and practical value
The emotion finding is specific and genuinely non-obvious. It isn't positive versus negative content that drives sharing, it's arousal. High-arousal emotions — awe, excitement, amusement, anger, anxiety — push people to pass things on. Low-arousal ones, including sadness and contentment, suppress it, even though both feel equally emotional from the inside. Awe turned out to be the strongest single positive predictor in the New York Times work, which is why long, ambitious, surprising pieces outperform light ones on sharing despite feeling like harder work. Berger goes further with an experiment showing that physiological arousal from an unrelated source — people who had just been jogging — increased sharing of content that had nothing to do with the exercise, which suggests the mechanism is closer to general activation than to specific feeling.
Public is the observation that behaviour which can be seen gets copied, and that a lot of good products are effectively invisible in use. Making the private public is a design decision: a distinctive silhouette, a logo oriented so onlookers can read it, a wristband, a moustache grown for a month. His broader phrase for this is 'built to show, built to grow'. He also uses public visibility to explain when social proof backfires — messaging that emphasises how many people are doing the wrong thing quietly tells the audience the wrong thing is normal, which is why a campaign about how many people steal from a park tends to increase theft.
Practical value is the most straightforward factor and the most available to small businesses with no budget: genuinely useful information gets passed on because sharing it helps the recipient, which earns the sharer credit for free. The chapter's most quotable takeaway is the framing arithmetic he calls the Rule of 100. Below £100, percentages sound larger; above it, pound amounts do. Take two illustrative offers of exactly the same generosity: £5 off a £25 item is 20% off, and 20% is the version people repeat. £80 off an £800 item is 10% off, and there the pounds win — nobody forwards a 10% discount, but plenty will mention eighty quid. The saving is identical in proportion; whether it spreads depends entirely on which side of £100 you're on and which way you write it.
Behavioural residue, and choosing a trigger properly
Two of Berger's practical refinements are worth more than the headline framework. The first is behavioural residue: the physical trace a product or a decision leaves behind after the moment of use has passed. A meal is invisible an hour later; a distinctive carrier bag, a wristband, a branded stamp card in a wallet, a sticker on a van all keep advertising long after the transaction. Berger's point is that this is a design decision rather than a marketing one, and cheap to make. If your business currently leaves no residue, ask what a customer could plausibly still be holding, wearing or displaying a week after they bought from you.
The second is that choosing a trigger involves a trade-off most people get wrong. A cue that fires very often but is only loosely associated with you is weaker than a cue that fires less often but is tightly linked, because a crowded cue has competitors and a tight association has none. Context matters too: the best triggers occur near the moment when the customer could actually act. A trigger tied to Sunday evening is worth little to a business that can only be booked in office hours. And the association has to be built deliberately and repeatedly — one campaign does not create a cue, which is why the ones that work tend to look boringly consistent from the outside.
Berger's cautionary case is the anti-drug campaign whose heavy repetition appears to have functioned as a reminder of drugs rather than a deterrent — a reminder that a trigger is neutral machinery. It fires whatever you attached to it, including the thing you were trying to argue against.
Stories are the vehicle, not a seventh factor
Berger's closing argument is that a story isn't another item on the list, it's the container that carries the other five. People repeat narratives, not facts, and a well-built story can smuggle social currency, a trigger, emotion and practical value along inside it. He uses the Trojan Horse image deliberately: the commercial point has to be structural to the story, load-bearing, so that it survives the retelling.
This produces the book's most useful warning, and the one most marketers ignore. Virality is worthless if the brand isn't part of the plot. Berger cites campaigns that racked up enormous view counts while sales went nowhere, because the thing people repeated — the joke, the image, the stunt — could be retold with the brand removed and lose nothing. The test he offers is simple and brutal: tell your story without naming the product, and see whether it still works. If it does, you have made entertainment for somebody else's benefit.
Key lessons
- Social currency: people share things that make them look good to others, so build something worth sharing for that reason.
- Triggers: build in environmental cues that remind people of your product at relevant moments.
- High-arousal emotions (awe, excitement, anger) drive sharing far more than low-arousal ones like contentment.
- Practical, useful value gets shared because sharing it genuinely helps the person receiving it, not just the sharer.
Word-of-mouth isn't random luck — it follows identifiable, research-backed patterns (STEPPS) that can be deliberately built into a product or campaign.
What this means for a UK small business
Triggers are the most actionable idea here for anyone with a small marketing budget, because they cost nothing but thought. Find something your customers already encounter constantly and attach yourself to it: the 31 January self assessment deadline, payday Friday, the first cold morning, the school run, the start of the new tax year in April. A payroll bureau that owns the last Friday of the month, or a café that owns rainy Mondays, gets recurring free recall that outperforms a much bigger ad spend.
Social currency explains why some UK small-business promotions land and others die quietly. A review request framed as 'please help us out' asks the customer for a favour. One framed around being the person who found the place first hands them something worth saying. The same applies to referral schemes: a discount code that makes the referrer look cheap converts far worse than one that makes them look generous to the friend.
And take the brand-in-the-story test seriously before commissioning anything clever. Plenty of UK small businesses have paid for a funny video that got shared widely and sold nothing, because the joke survived perfectly well without the company in it. Practical value is the safer bet at small scale: a genuinely useful checklist or calculator that carries your name gets forwarded internally by people you will never meet.
What’s aged well
The underlying psychological research holds up well and doesn't depend on any specific platform or trend.
What feels outdated
A few case studies reference platforms that have since faded, but the STEPPS framework itself is unaffected.
Where it falls short
The framework describes what correlates with sharing far better than it delivers what causes it, and the book's tone occasionally oversells how engineerable virality is. Ticking all six boxes raises your odds; it does not produce a hit, and Berger's own research is largely correlational — the New York Times analysis tells you what shared articles had in common, not what would happen if you added awe to yours.
The case studies have also dated fast. The blender videos, the specific 2010s campaigns and the pre-social-video examples now read as period pieces, and the STEPPS acronym is stretched — 'Public' and 'Social currency' overlap enough that the six factors feel like a packaging decision as much as a finding. It works best as a diagnostic for why something spread, rather than a formula for making something spread.
The Business Stuff verdict
One of the more rigorous, research-grounded marketing books on this list — genuinely explains the mechanics, not just the outcomes.
Three things to actually do after reading it
- Identify what social currency a customer gets from sharing your product, and make it more explicit.
- Build one environmental trigger that reminds customers of your product at a genuinely relevant moment.
- Review your last campaign for emotional intensity — low-arousal contentment rarely drives sharing.
If you liked this, read next
Five similar books
- Made to Stick (Chip & Dan Heath)
- Influence (Robert Cialdini)
- Purple Cow (Seth Godin)
- Predictably Irrational (Dan Ariely)
- This Is Marketing (Seth Godin)
Common questions
Can you actually engineer something to go viral using STEPPS?
No, and that's the honest answer the book slightly dodges. STEPPS raises your odds — content that carries social currency, attaches to a frequent trigger and provokes a high-arousal emotion is more likely to be passed on than content that doesn't — but the research behind it is correlational, drawn from analysing what shared material had in common rather than from making things spread on demand. Plenty of campaigns tick all six boxes and sink. The framework is far more valuable used backwards, as a diagnostic: when something of yours does spread, STEPPS tells you which lever did it, so you can do that deliberately next time instead of guessing.
Is Contagious still relevant when most of its examples are from the 2010s?
The mechanics have held up better than the examples. Blendtec videos and pre-TikTok campaign case studies read as period pieces now, and anyone reading for tactics will find them dated. But the underlying findings — that arousal rather than positivity drives sharing, that triggers beat one-off attention, that visible behaviour gets copied — are about human psychology rather than platforms, and short-form video has if anything made the arousal finding more obviously true. Read it for the six mechanisms and mentally substitute your own current examples. The chapter on triggers in particular has aged extremely well and is worth the book on its own.
How is this different from Made to Stick?
Made to Stick, by Chip and Dan Heath, is about whether an idea is remembered and understood; Contagious is about whether it gets passed on. They overlap around stories and emotion but answer different questions, and the Heaths' book is the better one on how to construct a message, while Berger's is better on what motivates somebody to forward it. If you're writing — a pitch, a talk, a piece of copy that has to stick in one person's head — read Made to Stick. If you're trying to get customers to tell other customers, read Contagious. Reading both is not wasteful; the practical overlap is maybe a fifth of each.
How long does it take to read?
Roughly five to six hours, and it's an easy read — one chapter per factor, each opening with a story and closing with a summary, so it's unusually skimmable for a research-based book. If you want the highest-value hour, read the triggers chapter and the stories chapter; those two contain the ideas most small businesses can act on immediately and most often get wrong. The introduction is worth reading properly too, because Berger's argument about influencers mattering less than the thing itself is the premise everything after it rests on, and it's the claim most marketing advice still contradicts.
