"If you want to win contest, your mind must be hard and joyless, like Russian turnip." - Sergei, American Dad
What he said. I'm reminded of that Chinese girl I saw on a documentary. She was maybe eight years old, but her and perhaps even more her father had only one thing on their mind: Olympic gold. She trained gymnastics severely for hours seven days a week, and had no time for fun or a social life.
Maybe one day at seventeen against great odds, she gets the medal. Now all her life so far has culminated, her goal is reached. So now what?
I can't say, but I know it's quite common for people who reach a major goal they have not thought beyond, to head for severe depression, just when they had thought they would be happiest.