The usual thing that you hear we tell kids is "you can be whatever you want to be" when it's really not entirely true. A more accurate saying might be, "you can be whatever you work hard at, even if you might not be the best." For adults, the line is, "do what you love."
What if you suck at what you love? If American Idol is any indication, passion doesn't always equal aptitude. Beyond American Idol, there are plenty of people that are always 'striking it out on their own' that are still doing so. There's plenty of actors and actresses that are waiters and waitresses. I suppose the assumption is that when you do what you love, you will spend time doing it, instead of going out, instead of playing video games, instead of watching TV. You'll keep going at it even after failure and rejected. And the biggest assumption is that you'll get better as you keep going at it.
So keep at it. And get better.
Wilhem has built Annologger, a tool that lets people worship your dentist appointments.