I've been talking with several people lately about why people (usually one or both of us in the conversation) won't do what they're passionate about. I'm not just talking about things you like; I'm talking about things you can't live without. Things that, no matter how tired and miserable you are, starting to talk about and work on them makes you light up.
Sometimes it's because you're afraid you'll find out you don't really love it. Or that you don't love something else you've previously professed to love. Maybe you like it a lot, but that's not the same. And if you leave what you say you love only to find you don't love the thing you left it for, what do you love?
I felt this way about art; I used to be "the kid who draws" in high school. I like it, and I'm not bad at realistic black-and-white sketches (here's an example of Scott; not a good one, but the only sketch of mine I could find online), but I'm not that good and not working on getting better now - and most importantly, I can live without it. There's a great quote from Uncle Vanya on this: "No, not knowing is better. At least there's still hope." (I realize it's more common to have these feelings about people than about academic disciplines.)
Knowing that you'll love something more with restricted exposure to it is different - and a good thing to know. I realize I woud loathe abstract mathematics if I had to do it for hours every day for years, which is why I'm not a theoretical mathematician. In small doses, for recreation, I adore it, hunger for it. I feel the same way about flourless chocolate cake. Terrible idea for my daily bread. Glorious special-occasion treat.
Sometimes you know you love something and should be going for it, but choose not to because of other obligations and responsibilities you value more. Sometimes you know you love something and you're going for it with a long-term plan - but it's easy to use that rationale as an excuse for avoiding questions you don't want to know the answers for.
If you know you don't want to know, and make that conscious choice and are all right with it - and choose the amount you're going to agonize over not-knowing this thing you've chosen not to know - then all right. That's a decision I may not agree with all the time, but it's one I can respect. You draw your own boundaries. "I need to whine for 5 minutes about this situation. Cut me off after that."
Love and passion, choice, uncertainty, control and recklessness, and the idea of knowing. I have been rather philosophical as of late. I step back to wrestle with these things when the going gets tough; dealing with this level of abstraction is easier, and it helps resolve reality into something I can deal with. The ability to go meta is like the "being able to fall safely" of the practice of being aware. It lets me see what's difficult, what hurts, and what I'm avoiding so that I can not avoid it. Being conscious of what I'm avoiding is a good way to eventually make myself face up to it.