In one of Alan Greenspan's books he says something along the lines that life is the pursuit of self-esteem and self-esteem needs constant nurturing.

I think that is pretty accurate. Past accomplishments only nurture self-esteem for so long. I wouldn't doubt Johnny Depp is completely miserable. There is just not much he can do tomorrow with how high the bar was set in his past. At least the average person can still dream the best is yet to come.

I am sure being a child prodigy is tough in the same sense.