The R Word
From the greenest beginner, to the most-published novelists, nobody likes rejections. But if you're in the game, they're bound to happen. As you learn the market and develop your craft, you can reduce but never completely eliminate them.
Rejection can mean anything from "you're kidding, right?" (loads of form rejections with no personal notes may mean you're pretty far off the mark), to "you can write, but you clearly haven't done your homework on our needs" to "oh, this is cool, but I don't know how to make enough filthy lucre on it to buy" to "this project's right, but the timing's wrong." Or they can mean nothing but the editor or agent involved was in a huge hurry to clean off her desk before vacation. Only rarely will they contain nuggets that will help you figure out how to make the project saleable. Honest, experienced critique partners, contest judges, and book doctors (sometimes, on all three) are more likely to provide those answers, but more often than not, you'll have to develop that intuition on your own.
You have to get over the idea that your writing project is your baby or a sliver of your psyche. You have to get past feeling so fragile that you let strangers tell you how you feel about your work... and even worse, yourself. I know talented writers who've never gotten anyplace because they couldn't develop a thick enough skin. Instead, they felt the pain of the rejections and stopped dead, afraid to risk such hurt again.
The writers who make it feel the pain, too, and all of them I've ever known experience moments (hours!) of self-doubt. But on the surface, they get tough as an old gator and keep charging the same door, not always from the same angle, but they ram their heads against it until they hear it splinter.
And when they succeed, that thick hide serves them well, because if you think it's tough getting rejections via mail or e-mail, wait until you have to deal with reviewers posting their ever-so-snarky "rejections" on the Internet or splashing them across the pages of Kirkus or PW. So think of your early rejections as tough love, preparing you for a tough business. Because that's what writing books is, make no mistake on that count.
For an excellent take on rejection, check out this post from author Karen McCullough guest blogging at Marilu Mann's Escape into the Fantasy. It's well worth reading and chock full of advice I wish I'd had when I was getting started.