Watch someone decide whether to enter a promotion and you’ll miss it if you blink. They see the flash — WIN A CAR, $10 cashback, scan to enter — and within a few seconds they’ve either reached for their phone or moved on. No spreadsheet, no deliberation. Just a fast, mostly unconscious judgement about whether this is worth the bother.
That judgement is the whole game. You can spend months on creative, media and prize budget, and it all gets compressed into the three seconds a shopper spends deciding if your offer is worth their time. At Trevor Services we’ve come to think of that moment as the 3-Second Equation — the shorthand from The Shelf Truth for the sum every shopper runs without realising they’re running it.
What is the 3-Second Equation?
The 3-Second Equation is the quick mental calculation a shopper makes when they see a promotion: Reward plus Belief, divided by Friction. How much do I want the prize? Do I genuinely believe I can win it? And how much effort will entering cost me? If the top of that sum outweighs the bottom, they enter. If it doesn’t, they scroll on — and no amount of media spend buys that decision back.
It’s deliberately crude. The point isn’t precision; it’s that all three terms have to work together. A brilliant prize nobody believes they’ll win fails. A winnable prize nobody wants fails. A genuinely appealing, winnable prize buried behind a ten-field form fails just as quietly. Most promotions that underperform aren’t broken in some exotic way — one of the three terms has quietly collapsed and taken the rest down with it.
Is the reward actually worth wanting?
Reward is the easiest term to get wrong, because it feels like the easiest to get right. Bigger prize, more appeal — except it doesn’t work like that. What matters is whether the reward clears the bar of being worth wanting at all. The Shelf Truth calls that floor the Insult Threshold: if the effort of claiming outweighs what’s on offer, you haven’t given someone a small reward, you’ve given them a small annoyance. A $2 saving that needs a receipt upload and a sign-in isn’t a modest win; it’s a reason to feel faintly insulted.
There’s also a quirk in how people value rewards that’s worth understanding. In a well-known set of experiments, Shampanier, Mazar and Ariely found that when a price drops to zero, demand jumps far more than the maths predicts — people don’t simply subtract cost from benefit, they treat “free” as a category of its own. That’s why a guaranteed gift with purchase can pull harder than a discount of similar value, and why a self-liquidating premium works at all. Reward isn’t only about size. It’s about how the brain files it.
Do people believe they can win?
Belief is the term most brands forget they can influence. A shopper looks at a single major prize and quietly concludes: not me, never me. The odds feel like zero whether they are or not. The Shelf Truth’s Rule of Three is a useful way to think about it — one prize reads as “impossible”, three prizes as “possible”, and a hundred small prizes as “probable”. Same total budget, very different sense of whether it’s worth a go.
That’s really a question of prize architecture: how you split a fixed prize pool to change what people believe about their chances. Our colleagues at Bamboo Marketing wrote about designing a prize structure worth entering, and it’s the other half of this term. The headline prize creates the desire; the spread of smaller, more believable wins is what turns that desire into entries. Of the live Australian promotions Trevor tracks, single-prize draws are comfortably the most common mechanic — which tells you how often brands lean on one big number and hope, rather than engineering belief. The fix is rarely a bigger prize. It’s a better-shaped one.
How do you reduce friction without gutting the entry?
Friction is where good promotions quietly bleed. Every field, every step, every “create an account to continue” is a small tax on entry, and the taxes compound. The instinct is to strip everything back to a single tap — but the evidence here is more interesting than “shorter is always better”. Venture Harbour’s review of form-length studies found cases where cutting fields actually reduced conversions: one optimiser removed fields and saw a 14% drop, because he’d cut the parts people were happy to fill in and left only the dull ones.
The more useful frame comes from BJ Fogg’s behaviour model, where action happens when motivation and ability meet at the right moment. Friction sits on the ability side, and it trades against motivation. A highly motivated entrant will tolerate a receipt upload; a merely curious one won’t tolerate a second screen. So the question isn’t “how few fields can we get away with” — it’s “how much friction have this reward and this belief earned the right to ask for”. A car draw can ask for more than a $5 cashback can, because the top of the equation is bigger. Some friction is also non-negotiable: receipt validation and fraud checks protect the promotion, and the job is to make necessary effort feel proportionate, not to pretend it away.
Working the whole equation, not one term
None of these terms is hard to grasp on its own. The mistake is treating them separately — polishing the prize while ignoring belief, or obsessing over a frictionless form attached to a reward nobody wants. The 3-Second Equation earns its keep because it forces you to hold all three at once, and to be honest about which one is dragging.
It also pairs neatly with the One Job Rule: once you know the single job a promotion is doing — trial, frequency, basket, data — you know which term to weight. A data-capture promotion can carry more friction; a trial promotion can’t afford any. This is the kind of pre-launch pressure-testing Trudy, Trevor’s predictive promotional intelligence platform, is built for — running a mechanic against thousands of past campaigns before a dollar is committed.
So if you’re sketching out a promotion and something feels off but you can’t quite name it, try running it through the equation. Usually one of the three terms has collapsed and you just hadn’t spotted which. If you’d like a hand pressure-testing the idea before it goes live, we’re happy to talk it through.
