2. This answer will sound useless, but it's the same reason anyone is good at anything. There's no single secret. There are about 20 different things we have to do, from recognizing talent to talking about product ideas to matching people up with VCs, and we try hard to do them all well.
3. By accident. When we first started YC, we didn't know what to do, so we started with a summer program. Most college students regard summer jobs as disposable anyway, so we figured no one would mind if the experiment was a disaster and all the companies failed. As it turned out, that batch did remarkably well.
4. This one I already did write about: http://ycombinator.com/about.html
5. That it's not as easy as it looks. A lot of people think investing is like betting on horses: you pick, they race, and if they win you get money. Actually it is a lot more active than that. And the earlier the stage, the more work it is. If you want to invest at this stage, you need to have the same qualities you'd need to be a successful founder.