Based on what evidence do you say this? Not trolling, really curious. I seem to recall (but don't have references on hand, so fell free to discard this) that people tend to be WORSE at honest self-evaluation the greater their success. They tend to get wrapped up in their own 'press' and surrounded by people constantly telling them how awesome they are, how much smarter than everyone else, etc..
Compare: "Product A was terrible and we are embarrassed to have released it" vs "Product A was a good start and proved that there's a market, and we've learned a lot that's going to get you really excited for Product B."
One last thing that I'm adding after posting this is that I also don't think this means successful people don't succumb to feelings of anger, hurt pride, revenge fantansies and all the other normal human stuff. Just that eventually you get past that and learn from it.