People who support themselves by trading successfully are likely working for a company (bank or hedge fund, etc). Often they are dealers, who make money on the bid-ask spread, so they don't bear as much risk as (say) traders working on prop desks. These depend more on the success of their trades for their income, but even so they get a non-negative income. Now, independent day traders working in their underwear is a different story. Not only they bear all the risk of their trades, they're likely "losers" (in the game theory sense) in average.