Why Do We Misremember the Pain of a Colonoscopy?

Daniel Kahneman, psychologist and Nobel laureate in Economics, describes in Thinking, Fast and Slow (2011) a real experiment, designed together with physician and researcher Don Redelmeier of the University of Toronto, that revealed something fairly counterintuitive about how the memory of pain works: we don’t remember the total amount of suffering we experienced, but a much simpler, and in some ways misleading, summary of that experience.

The experiment: 154 patients and a pain scale every 60 seconds

The study was conducted with 154 patients undergoing a colonoscopy, at a time before this procedure was routinely performed under anesthesia. Every 60 seconds, patients were asked to rate their pain level at that exact moment, on a scale from 0 (no pain) to 10 (unbearable pain). The procedure’s duration varied widely from patient to patient: the shortest lasted 4 minutes, the longest, 69 minutes.

When it was over, each patient was asked how much total pain they felt they’d experienced during the whole procedure.

Two patients, two very different experiences

Kahneman illustrates the finding by comparing two specific patients from the study:

• Patient A: the procedure lasted 8 minutes. His last pain reading, right before it ended, was 7 out of 10.
• Patient B: the procedure lasted 24 minutes, three times longer than Patient A’s. His last pain reading, right before it ended, was only 1 out of 10.

If you add up the pain moment by moment across the entire procedure (what Kahneman calls the “area under the curve”), there’s no doubt: Patient B, having been exposed for much longer to comparable pain levels, objectively suffered more in total than Patient A.

The result that didn’t match the logic

However, when both patients were asked how much pain they remembered feeling in total, the result was the opposite of what you’d expect: Patient A remembered the experience worse than Patient B, despite having objectively suffered considerably less total time of pain.

Statistical analysis of the 154 patients revealed two systematic patterns, which Kahneman named:

• Peak-end rule: the retrospective rating of a painful experience is explained mostly by the average between the worst moment experienced (the peak) and the pain level right at the end (the end).
• Duration neglect: how long the experience actually lasted barely influences the later memory of it.

Applying this rule to the two patients: both had the same pain peak (8 out of 10) at some point during the procedure. But the average between that peak and the final level was 7.5 for Patient A and only 4.5 for Patient B. Patient A simply had the bad luck that his procedure ended at a moment of high pain, and that alone was enough to leave him with a worse overall memory, regardless of having suffered less total time than Patient B.

Two different ways of measuring the same thing

Kahneman calls hedonimetric totals the real sum of pain moment by moment (what an outside observer would calculate by adding up all the readings), and distinguishes them from retrospective assessments, which is what each patient remembers afterward. His conclusion is that these two measures can be systematically different: the first weighs every minute of the experience equally; the second only really pays attention to two specific instants, the worst and the last.

This led Kahneman to draw a distinction he developed further in the rest of the book: the difference between the experiencing self, which lives each moment separately, and the remembering self, which later builds a summarized story of the whole experience, and which is the one that, in practice, decides whether we’d repeat something or not. The two “selves” don’t always agree on how much was really suffered.

A practical implication for medicine

The book itself points to a direct consequence for clinical practice: if the goal is for the patient to remember the procedure as less painful, the most efficient move isn’t necessarily shortening its duration, but making sure it ends at a moment of lower pain intensity, even if that means extending the procedure a few extra minutes with a gentler final phase. Reducing the pain peak, by this logic, weighs more in the final memory than reducing the total exposure time.

This same mismatch between what’s experienced and what’s remembered shows up in many everyday decisions that have nothing to do with medicine, from how a trip or a job is evaluated to how a more analytical profile or a more intuitive one judges afterward whether an experience was worth it, a judgment that rarely rests on the real sum of what was actually lived.