Mike Downey: What's your biggest regret of your entire life? He says a 1998 psychological review paper by Tom Gillovich, Danny Kahneman and Victoria Houston Medvech asked people to think about their regrets. The way they studied it is as straightforward as can be, he says. But in other words, the way to study a regret is usually just to ask people, hey, tell me about something that you did thatYou didn't do.