You suggest that the lesson should be based on the outcome, but actually in the presence of significant random noise/unknowns, that's not always true. It's qui

You suggest that the lesson should be based on the outcome, but actually in the presence of significant random noise/unknowns, that's not always true. It's quite possible to make bad decisions that turn out well and good decisions that turn out badly. To learn the correct lessons, he needs to work out if his original plan was sensible given what he knew (or could reasonably find out) at the time and he's just unlucky, or if the decision to invest was reckless or based on inadequate or wrong information. Having said that, it's so easy to deceive ourselves, that I've heard people say that it's a good idea to work out what would falsify your assumptions before investing. The decision he made was either a good one or a bad one based on the information available to him at the time. That will be true regardless of whether he becomes a billionaire in the next month or goes entirely broke. The true lesson to be learned is not dependent on the outcome.