As writers, we will have to deal with rejection at some point in our lives. (Unless you never come out of your Writing Cave.)
However, I think it's important to remember that rejection can provide some important life lessons.
For example, let's take a quick trip down memory lane and see how one person decided to deal with it:
Scene: A crisp fall evening. Two students are walking through campus.
Young Effy: I suspect that you are planning to ask me out on a date. Since I'm not interested in dating anyone at the moment, I'd advise you against doing so, because I'm going to say no, and I'd hate to hurt your feelings.
College Boy: I know. I'm still going to ask you out.
Young Effy: I don't think you're hearing me correctly.
College Boy: I heard you correctly and I don't care. I'm still going to ask you out.
Young Effy: *harrumphs and crosses arms*
You see, College Boy has no fear of rejection here. Absolutely none. He even knows that there's a good chance Young Effy will turn him down, but he doesn't care. He's taking life by the horns.
So what happened to Young Effy and College Boy? After a while Young Effy finally caved and went on a date with College Boy and, guess what, now they're married.
Don't let the fear of rejection keep you from going after the things you want most in life.
Now, go finish your manuscript and send a query letter or two. Or twenty.