Fun fact: Mew2King played Fox in Melee, owned everyone, then started playing Marth and continued to own everyone. When I asked him why he was playing Marth instead of Fox if Fox was supposed to be better, he said "Fox is too hard. You mess up sometimes" and it's true. You'll make mistakes with Fox because you can't be on the ball all the time, and it only takes one mistake to lose a stock.
When I asked him how he got so good, he responded with "I just play all the time and don't do anything else" at FC:Diamond.
Simple, simple stuff.