Writing is a series of raised hopes and crushed dreams. Ok, so maybe I'm being dramatic, but some days it doesn't feel like it.
Just by it's very nature, writing is a very tumultuous process. Or perhaps I mean the process of getting published, but for many people it's much the same thing.
You write something. You think it's amazing. You read it again, and think it's crap. Then you do some editing. And maybe some more editing, and what the heck, maybe a bit more. And by the time you're done you can't help but think, "You know this is pretty darn good."
So you put together your query letter (and maybe synopsis). You agonize over it and edit the crap out of it. And then you put yourself out there.
You think to yourself, "I think I really have something this time."
And then you start to get the rejection letters. That's when you realize, "Maybe I just don't have it. Maybe this isn't something I can do after all. Maybe I should just curl up into a little ball and feel sorry for myself."
And then, of course, a few days later (or hours or weeks, depending on just how much spring back you've got in you), you put out a few more query letters and hope springs anew. Because if you don't keep trying you're never going to get anywhere.
Seriously, it's amazing there aren't more medicated writers out there.