What’s the point of striving for mediocrity?

People who just do “voo and chill” and say “you can never beat the market. I mean clearly there are some successful day traders in the world. Even if your not day trading, buffet even said “concentration creates wealth, diversification keeps it”. I don’t get why somebody wouldn’t try to make more than 8-10% and to create wealth with certain high conviction stocks. What’s the point of believing so little in yourself that you are fine working a job making in the range of 60-120k a year and making 8-10%. What’s the point for striving for mediocrity? Just genuinely curious about the mindset. Is it fear? Lack of confidence? If somebody told me 10% of traders make money and 90% lose I automatically think to myself, we’ll why can’t I be that 10%? Did those 90% really put in the time and effort required? Of course not. A large percentage probably quit after a few months.