Duration Neglect
How long something lasted has almost no bearing on how it is remembered or scored afterwards. That is duration neglect, and it is the sturdier half of a famous pair. Its sibling, the peak-end rule, says which moments get kept. This one says what gets thrown away, and what gets thrown away is the quantity of the experience itself, which is the part a person actually lived through. The finding belongs to Barbara Fredrickson and Daniel Kahneman, 1993, with Fredrickson as first author, and popular writing attributes it to Kahneman alone.
What it is
The distinction that makes this more than a memory quirk is that duration is not merely underweighted. In the best-known clinical data it played no part at all.
The credit, stated properly, because this site got it wrong twice. The field first read "Kahneman alone". On 2 September 2026 it was corrected to "Redelmeier and Kahneman", which fixed the famous-name problem and created a chronology problem, because Redelmeier's papers are the medical applications and they come later. Duration neglect and the snapshot model of remembered experience are established by Fredrickson and Kahneman in 1993, three years before the colonoscopy paper. Logged in the open, because a vault that silently corrects itself twice is doing exactly what this publication criticises other people for.
The original evidence was never only the colonoscopy study. Fredrickson and Kahneman's first study had 32 people rating pleasant and unpleasant film clips moment by moment, and 96 more ranking the clips afterwards. Longer unpleasant clips were rated about the same as shorter ones. What predicted the verdict was the worst moment and the last moment, not the running time.