In the short run, a great deal of investment success can result from just being in the right place at the right time. I always say the keys to profit are aggressiveness, timing and skill, and someone who has enough aggressiveness at the right time doesn't need much skill.
At a given time in the markets, the most profitable traders are likely to be those that are best fit to the latest cycle. This does not happen too often with dentists or pianists—because of the nature of randomness.
The easy way to see this is that in boom times, the highest returns often go to those who take the most risk. That doesn't say anything about their being the best investors.