A Modern Guide to Thinking, Fast and Slow
Part V - Two Selves
Chapter 35: Two Selves
Overview
“Utility” has two distinct meanings: experienced utility (pleasure and pain as they unfold) and decision utility (the anticipated pleasure or pain we'll get from a choice). There is a systematic mismatch between the two. Memory does not record experiences by summing moments over time. Retrospective judgments overweight the worst (or best) moment and the ending while largely ignoring how long the episode lasted.
This creates a conflict between two selves: the experiencing self, which lives the moments, and the remembering self, which evaluates them and then governs future decisions. Because choice is driven more by remembered episodes than by duration-weighted experience, people can end up optimizing for better memories rather than better lived experience and sometimes choose an objectively worse experience because it will be remembered as less bad.
Replication & Reliability
The peak-end rule and duration neglect in retrospective pain evaluations are well supported in short, well-defined episodes. The book’s core evidence comes from the colonoscopy study (Redelmeier & Kahneman, 1996) and a follow-up randomized trial that manipulated the ending of colonoscopy (Redelmeier, Katz, & Kahneman, 2003). A large meta-analysis of 174 effect sizes (Alaybek et al., 2022) found that the peak-end rule was robust across boundary conditions and that the effect of the duration was essentially nil, supporting the idea of duration neglect.
However, the peak-end rule appears less predictive for extended, multi-episode experiences (e.g., remembering vacations or “the previous day”), where other summaries can perform as well or better (Kemp et al., 2008; Miron-Shatz, 2009).
Recommendation
This chapter’s conclusions are best applied to short, well-defined episodes, where the peak-end rule and duration neglect are best supported. Be cautious about generalizing to extended, multi-episode experiences, where peak-end is often a weaker predictor and other summaries can matter as much or more.
Chapter 36: Life as a Story
Coming soon
Chapter 37: Experienced Well-Being
Coming soon
Chapter 38: Thinking About Life
Coming Soon
