If you're a writer, rejection is part of the job--it happens to all writers, no matter how talented. When--not if, but when--it happens, there are several ways to react. Some writers I know get down for a day or two, then forget about it. Others brush off a rejection as nothing. Still others will mull it over for weeks at a time, picking apart each word from the editor or agent who rejected the project, trying to figure out what went wrong. Some writers head straight for the pint of Ben & Jerry's.
I don't fall into any of these camps.
I admit, I've gone for ice cream after a rejection letter appeared in my in-box, but I will use any excuse for ice cream (selling a book, seeing the cover for the first time, getting good news or bad from an editor, the Red Sox winning a big game, you name it.) When I get a rejection letter, rather than bemoan it, I view it as one person's opinion that a particular project isn't right for the market at this time. When viewed that way, it doesn't bother me. It's nothing more than a simple business decision. I haven't been fired; I've essentially been told to try to come up with something more marketable. So in the end, my internal response to rejection is, "Okay. Thanks for the analysis."
When I first started writing, it was tough to do that. No writer wants to think that the time and energy consumed by that rejected project was wasted. But over the years, I've learned that markets change, editors change, and readers' tastes change. As long as I keep working hard to become a better writer, improving my craft with each project, by the time the market is ready for that particular idea, I can resubmit, possibly in an improved version. Even if it doesn't sell, I can always pull a character, a story thread, or some other component of that project and use it in the future. In the meantime, I don't stand still. I keep writing. By the time I receive a rejection, chances are that I have another project--maybe even two or three--in the works, and a new focus for my energy.