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🎬 Why do we finish a bad film?

A ticket booth that sold the same seat at three prices, a memory effect that did not survive meta-analysis, and a wasp that cannot count. Why the thing holding you in the seat is probably not the money you paid.

4
lessons
~12 min
to learn
Adults
level
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What you’ll learn

  1. The Ticket Is Already GoneDefine a sunk cost precisely, and see it measured on real people in a real theatre.The ticket price and the minutes already spent are unrecoverable whatever you choose next — and a field experiment that changed what patrons paid, at random, shows how much that still moves behaviour, and for how long.
  2. Why Leaving Feels Like LosingSeparate the three things that make standing up feel expensive: finality, self-image, and the people beside you.Walking out converts an open case into a settled loss, concedes that the choice was poor, and does both in front of witnesses — none of which is about the ticket at all.
  3. The Pull of the EndingReplace the folk story about unfinished business with what the evidence actually supports: nearness to the end, not cost already sunk.The famous Zeigarnik memory effect does not survive meta-analysis, but the pull to resume and complete does — and when researchers vary sunk cost and completion separately, completion is what moves the decision.
  4. How Much of This Is Actually TrueWeigh the evidence honestly, distinguish the past as a debt from the past as evidence, and apply a forward-looking test.The money effect is solid but modest, the time effect is genuinely contested, and a wasp that cannot count shows why acting on what you have already invested is sometimes an estimate rather than an error.

Questions this course answers

Halfway through the film, which of these is the sunk cost?

The payment cannot be recovered by any choice you now make, so it carries no information about what to do next. The other three are all still ahead of you, and all three belong in the decision.

Arkes and Blumer's full-price season-ticket holders attended about 4.1 of the first five plays. How many did the randomly discounted groups attend?

About 3.3 — roughly eight tenths of a play fewer, from nothing but an unannounced discount. In the second half of the season the gap disappeared entirely.

Conlon and Garland varied sunk cost and nearness-to-completion separately. Which one moved people's decisions?

Told a project was nearly finished, people kept funding it. Told a lot had already been spent, with completion held constant, they barely moved. The 2012 review warned that much earlier sunk-cost research had been measuring completion without realising it.

Match each pressure to what it actually makes salient

Four different pressures can push toward the identical action — staying in the seat — while each one is responding to a completely different feature of the situation.

Put the stranger's-offer test in order

The first step is only there to clear the past off the table. The decision itself is made entirely out of the last three.

Why is a bad film you have already sat through for an hour still worth something to your decision — even though the hour itself is unrecoverable?

This is the distinction the digger wasp illustrates. Her own investment is the only measurement of the burrow's contents she can make, so acting on it is not a fallacy — it is an estimate. Your hour works the same way: it tells you a great deal about the next hour.

Grounded in trusted sources

  • Arkes, H. R., & Blumer, C. (1985). The psychology of sunk cost. Organizational Behavior and Human Decision Processes, 35(1), 124–140 — https://doi.org/10.1016/0749-5978(85)90049-4 (Experiment 2: the Ohio University Theater season-ticket field experiment, the three randomly assigned prices, the colour-coded stubs and the first-half/second-half split)
  • Arkes, H. R., & Ayton, P. (1999). The sunk cost and Concorde effects: Are humans less rational than lower animals? Psychological Bulletin, 125(5), 591–600 — https://doi.org/10.1037/0033-2909.125.5.591 (no clear case in non-humans as of 1999; young children outperforming adults; the overgeneralised 'don't waste' rule)
  • Soman, D. (2001). The mental accounting of sunk time costs: Why time is not like money. Journal of Behavioral Decision Making, 14(3), 169–185 — https://doi.org/10.1002/bdm.370
  • Navarro, A. D., & Fantino, E. (2005). The sunk cost effect in pigeons and humans. Journal of the Experimental Analysis of Behavior, 83(1), 1–13 — https://pmc.ncbi.nlm.nih.gov/articles/PMC1193697/ (and Navarro & Fantino, 2009, The sunk-time effect: an exploration)
  • Petrov, N. B., Chan, Y. K. M., Lau, C. N., Kwok, T. H., Chow, L. C. E., Lo, W. Y., Song, W., & Feldman, G. (2023). Sunk cost effects for time versus money: replication and extensions registered report of Soman (2001). International Review of Social Psychology, 36(1), 17 — https://doi.org/10.5334/irsp.883 (821 participants; mixed support — the time/money difference replicated in one study, sunk cost effects appeared in both domains in another)
  • Conlon, E. J., & Garland, H. (1993). The role of project completion information in resource allocation decisions. Academy of Management Journal, 36(2), 402–413; and Garland, H., & Conlon, D. E. (1998). Too close to quit: the role of project completion in maintaining commitment. Journal of Applied Social Psychology, 28(22), 2025–2048 — https://doi.org/10.1111/j.1559-1816.1998.tb01359.x (note: two different Conlons — E. J. Conlon on the 1993 paper, D. E. Conlon on the 1998 one, which is why the cards name surnames only)
  • Sleesman, D. J., Conlon, D. E., McNamara, G., & Miles, J. E. (2012). Cleaning up the big muddy: a meta-analytic review of the determinants of escalation of commitment. Academy of Management Journal, 55(3), 541–562 — https://doi.org/10.5465/amj.2010.0696 (sunk cost: 34 independent samples, 5,524 units, true-score correlation ≈ .24; sunk cost, self-justification and project completion as the three most-studied determinants)
  • Ghibellini, R., & Meier, B. (2025). Interruption, recall and resumption: a meta-analysis of the Zeigarnik and Ovsiankina effects. Humanities and Social Sciences Communications, 12(1), article 962 — https://doi.org/10.1057/s41599-025-05000-w (59 publications; no memory advantage for interrupted tasks once Zeigarnik's own data are excluded; resumption around 67% across 21 studies)

Every Wunder lesson is built from real, reputable sources — never invented.

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