The number of times this ever happens is outweighed a millionfold by the frequency of times where people incorrectly believe this to be the case.
What happens in the vast majority of cases is that people believe they’re making money, but after fees are actually losing to index funds. Or people believe they’re making money, but lose their shirts the moment the market turns sideways. Or people do succeed due to completely random chance, but the level of risk they took on to make that return is significantly higher than other investments with comparable returns.