Good experience, and bad

It's an old cliche that experience is the best teacher. While that is no doubt true, the pithy saying hides a big complication - bad experiences are a good teacher while good experiences are bad teachers. The other day, I read someone's tweet that in a bull run, everyone's IQ is 30 points higher, which points to the problem. If someone starts investing and then for many months and years the going is good and the markets are going up, then they would have gained no experience at all. In fact, they would have a negative experience, in the sense of almost certainly being a worse investor than at the beginning. When one starts investing and only good times follow for a while, then one gets a distorted view of rea