when i was a kid i did a black flip and hit my head on a diving board. ever since then i can't do a black flip. it's a psychological thing. before you get knocked out, you don't think about getting knocked out. you don't think it can happen to you. but once it does, you know that it can happen again.
look at fernando vargas. he was so confident and sure of himself. larry merchant said that he had an "aura of invisibility". then trinidad knocks him out. and he was never the same. i believe he was too young and had to few fights to be physically shot. i think he lost confidence his confidence.