Don't cry over spilt milk. Everyone's heard that.
In fact, I have actually spilled milk. Depending on where it gets spilled, if you're not careful, it can leave a pretty sour smell, especially in weird corners of a car's carpet. Anyway, the best thing to do is clean it up and forget about it as soon as possible.
That applies to writing as well. I've received my share of manuscript rejections, as many authors have. That doesn't stop me. If the rejection contains constructive criticism, I follow the advise gladly and clean up my manuscript so it's ready to go out somewhere else.
What about you? Do rejections paralyze you, or do consider them challenges to progress as a writer? Please share.