Excellent essay by Paul Graham, in his usual left-brain-heavy style:
I suspect a lot of people aren’t sure what’s the top idea in their mind at any given time. I’m often mistaken about it. I tend to think it’s the idea I’d want to be the top one, rather than the one that is. But it’s easy to figure this out: just take a shower. What topic do your thoughts keep returning to? If it’s not what you want to be thinking about, you may want to change something.
To me, it’s all about doing something that you’re truly passionate about, not just pretend make-believe passionate about, because you think you have to, or you hope it’ll lead to something down the line (fame and money, anyone?).