How many people out of 100 average americans do you think have the acuity to beat the market averages on an annual basis. 80% of mutual funds cannot do it. Maybe 1 or 2 - most will lose if they try.
How many people out of 100,000 have the ability to gain 100%+ per year on average. Maybe 1 or 2.
Essentially you require high level mathematical/analytical skills. In combination with a "balanced" ego - you need to be able to eat it quite a bit. Probably jet fighter pilots would not be good candidates for traders. NFL quarterbacks OTOH maybe so. You've got to immediately forget about those sacks and interceptions to go back out there and perform.