I started playing because the game is fun, and I was convinced I could beat it.
I kept playing because it was fun, and because I could indeed beat it.
I stopped playing when it wasn't fun anymore (even though at that time it was more profitable than my day job).
Now, a seven-year hiatus later, I play again because it's fun again. But now the money is not a motivation anymore.
Doesn't mean that my competitive nature doesn't want me to improve and win, though.