Simple, compare a large number of investors based on some criteria with the overall average.
AKA, if you think there are people that do better than average, then picking people who have beaten the odds for 10 years and see how they do over the next 10 years. Repeat over a few decades.
There are things that seem to work. The most common way to 'beat the market' is trading a low chance and ideally hidden chance of failure for inflated returns. EX: A 1 percent change of losing 95% of your investment should be worth lot's of money on good years. This is really appealing when investing other peoples money as you don't share in their downside.
AKA, if you think there are people that do better than average, then picking people who have beaten the odds for 10 years and see how they do over the next 10 years. Repeat over a few decades.
There are things that seem to work. The most common way to 'beat the market' is trading a low chance and ideally hidden chance of failure for inflated returns. EX: A 1 percent change of losing 95% of your investment should be worth lot's of money on good years. This is really appealing when investing other peoples money as you don't share in their downside.