Of course, we writers have known for a long time that rejection (of our work) hurts. It can make us question our writing, our talents, even ourselves.
Playing devil's advocate for a second -- rejections can be extremely worthwhile, possibly telling us something that might be wrong with our novel. That there should be a change made, perhaps several, before sending the work out again. Rejections can tell us that our work just isn't ready.
But, okay, sure. Sometimes, rejections are simply a matter of opinion. One agent's/editor's subjective decision not to pursue our work. Sometimes, it's just a matter of the right one coming along at the right time (yes, I know exactly how cliched that sounds) while waiting through the rejections.
Ultimately, I think it's how we handle the rejections that matters most. Do we let 'em cripple us for more than a few minutes? Do we let 'em stop us from trying again? Do we decide that "x" number of rejections means we'll never, ever, in a million, zillion years be published?? If the answer is "yes," then I think they win. The rejections. I think if they make us give up on our dreams so easily, then they win. I can picture them laughing, pointing at us, mocking us - for giving up so quickly.
It's up to the writer, to decide how to handle the pain of rejection. And, yes. It's going to sting. Sometimes badly. But it can also make you try harder. It can make you dig in, get stubborn, decide to defy the odds. To be the underdog who never, ever gave up.
Where's that Rocky theme song when I need it? Ahh....here it is!