You know, when I want to ask someone out, all you have to ask is, "Reasonably, what's the worst that could happen? She'd say no, things MAY be awkward for a bit, if she's shallow enough to let that happen, and then you can go back to being friends." Then just go and ask her out. If she says no, get over it. It's not the end of the world, there's billions of other girls out there anyway.
Of course, you can keep trying, if you really think she's that special, or have nothing better to do, but some may consider that stalking if it gets too out of hand.
So yeah, I've been rejected before, but I never really let it get to me, not anymore. Hell, I was at a party a few nights ago and essentially got rejected twice. That didn't stop me from enjoying the rest of the night, either. It's just something you gotta go through.
I mean, going back to Sam's statement, you'd rather put yourself out there for a chance at something good rather than go through life alone, wouldn't you? To put it in extremes, at least.