Richard E. Nisbett answers this year’s Edge question, What is your dangerous idea?, with the notion “that people are very unreliable informants about why they behaved as they did, made the judgment they did, or liked or disliked something”:
Does it matter that we often don’t know what goes on in our heads and yet believe that we do? Well, for starters, it means that we often can’t answer accurately crucial questions about what makes us happy and what makes us unhappy. A social psychologist asked Harvard women to keep a daily record for two months of their mood states and also to record a number of potentially relevant factors in their lives including amount of sleep the night before, the weather, general state of health, sexual activity, and day of the week (Monday blues? TGIF?). At the end of the period, subjects were asked to tell the experimenters how much each of these factors tended to influence their mood over the two month period. The results? Women’s reports of what influenced their moods were uncorrelated with what they had reported on a daily basis. If a woman thought that her sexual activity had a big effect, a check of her daily reports was just as likely to show that it had no effect as that it did. To really rub it in, the psychologist asked her subjects to report what influenced the moods of someone they didn’t know: She found that accuracy was just as great when a woman was rated by a stranger as when rated by the woman herself!