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Memories are story shaped. As are understandings. To remember, or make sense of, a thing is to have a story about it. Colonoscopies and correcting cathartic errors can probe the inner workings of these stored stories. Memories aren't machine-like recordings. They resemble movies more than raw footage. They are carefully lit and edited. Daniel Kahneman says of this filtering and forming, that "Confusing experience with the memory of it is a compelling cognitive illusion." Kahneman used colonoscopies to illuminate the ends of human memory. Comparing how conscious colonoscopy patients rated their experience of pain every 60 seconds during the procedure with how they recalled the total amount of pain, resulted in "two principles of memory." First "duration neglect" whereby the time the procedure took had no effect on recalled pain. Second the "peak end rule," recalled ratings depended only on the peak of pain and it's level at the end of the procedure. So memories, and decisions based on them, are often "not correctly attuned to experience." Our experiencing self often has adaptive amnesia. The raw footage of most experience isn't important, but we evolved to find emotionally significant events worthy of stories and storage. "The same core features appear in the rules of narratives and in the memories of colonoscopies, vacations, and films." It makes sense that "Duration neglect is normal in a story, and the ending often crucial." Stories can change our health, physically and mentally. Jamie Pennebaker's research shows certain kinds of disclosure can reduce the health-damaging effects of past trauma. He asked subjects to write about their "most upsetting or traumatic experience," for just 15 minutes on four consecutive days, then tracked their health for a year. Those whose stories showed increasing understanding over the four days had significantly fewer illnesses than those who simply repeated the story they started with. The key wasn't expressing themselves, or venting emotions, but rather making new sense of their situations, changing their explanatory story. Though popularly believed, Jonathan Haidt says there is no evidence for catharsis having therapeutic effects. Catharsis rehearses and trains the prior state. Whereas therapy should cause a change. Alter the old story. Many would find disturbing the combination of: Steven Pinker's "to a very great extent our memories are ourselves," Kahneman's "I am my remembering self and the experiencing self who does my living is like a stranger to me," and Oliver Sacks's observation that we have "no mechanism in the mind or the brain for ensuring the truth...of our recollections.". Many fear that stories mislead. But stories are how our memories and understanding works. By all means get better stories. But don't tell yourself the tall tale that you can do without them. Illustration by Julia Suits, The New Yorker Cartoonist & author of The Extraordinary Catalog of Peculiar Inventions. Previously in this series: Kahneman and Bentham's Bucket of Happiness Kahneman's Clarity: Using Mysterious Coinage in Science What Rational Really Means The Cognitive Science of Star Trek