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There’s a moment in a lot of setup flows that does more persuasive work than any button copy you’ll ever write. It’s the moment a user notices they’re four steps into a six-step process — and what’s working on them isn’t the finish line ahead. It’s the trail behind them. The effort they’ve already put in starts arguing your case, in a voice most people find oddly hard to talk back to.

Economists have a name for the force underneath that moment, and — tellingly — they mostly describe it as a mistake. The sunk-cost fallacy is our tendency to keep pouring resources into something because of what we’ve already spent, even when a clear-eyed look at the future says stop. Hal Arkes and Catherine Blumer laid it out cleanly in 1985: people sit through a film they’ve stopped enjoying because the ticket is paid for, finish a meal they no longer want, keep a doomed project breathing because shutting it down would “waste” the year already sunk into it. The spent cost is gone in every version of the future. It shouldn’t touch the decision. It reliably does.

Notice what that means for a product. Reluctance-to-waste isn’t something you install — it’s something your user walks in already carrying. The design question is only which way it points.

Point it well and it’s one of the kindest forces in your toolkit. A migration that stalls halfway is worse than useless — the user has a half-imported mess and nothing to show for it. Reminding them how far they’ve come (“4 of 6 — you’re almost through”) gives their own reluctance-to-waste a job worth doing: finishing a thing that will actually serve them. Non-empty checklists, restore-where-you-left-off, a saved draft that greets them by name — these all lean on the same instinct, and when the remaining work pays off, everyone wins.

Point it badly and you’re charging rent on a bias. The tell is simple, and it’s a question about them, not you: is the work that’s left genuinely worth their time? If finishing the setup unlocks something they came for, surfacing their progress is a favor. If you’re stacking steps mostly so the accumulating effort makes quitting feel like a loss — a six-field form where two fields would do, a wizard padded to look substantial — then you’ve turned their instinct against them. They’ll finish, resent it dimly, and trust you a little less next time. Sunk cost completes the flow; it doesn’t build goodwill.

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Here’s the part builders miss, because it’s aimed at us. The same bias that keeps a user in your funnel keeps you in a bad feature. Barry Staw called it escalation of commitment: the more you’ve invested in a course of action, the harder it is to abandon, precisely because you’ve invested. The quarter you sank into the feature nobody uses is the reason it’s still on the roadmap. The rewrite that’s “80% done” has been 80% done for two months. The months already spent feel like a reason to keep going. They’re not — they’re gone either way. The only question that survives an honest look is the same one you’d put to your user: is what’s left worth the time it’ll cost?

So the discipline cuts both ways. Show a user their progress when the finish is a gift, and stay quiet when it’s a trap. And every so often, run the same test on your own roadmap — because the effort you’ve already spent is the one argument that sounds like wisdom and is usually just weight.