Ask HN: How do you focus your studies?

I think many of you out there are like me in that I am a super curious person. I love to learn about how things work and why they are so. Specifically, many areas of computer science greatly interest me. The downside to this is that I end up spending equal time on many different areas and am left being "decent" at a couple things but not "great" at anything, which makes me feel like I don't have a lot of value. I have the capability and the drive to be really good at something if I could just decide on a single path worth pursuing.

If you are/were like me, I want to hear your personal experiences in how you picked something to focus on and if you would do it the same way if you had to start over.

If it makes any difference, I am 21 years old majoring in CS. I have made it a point to try out CS classes in several different areas throughout my stay here. Also, I do not plan on going the PhD or large company route: I like the idea of startups.