This is one of those concepts that seems counterintuitive but is in fact one of the most empowering ideas a writer can have, and I know whereof I speak on the rejections front.
I've had something like 410 rejection letters over the course of my career to date. I sold my first short after 96 rejections for various shorts and novels and my first book after about 360.
Rejection happens. It hurts. It's also a point of pride, not something to be bummed about. Here's why:
Finishing and submitting a story means you're in the game and you should be proud of that. Rejections are a measure of finishing and submitting a story—you can't get one without the others. So, getting a rejection means you're in the game. Be proud of that. How many people do you know who say they want to write but don't? How many who start things and never finish them? How many who finish, but won't send something out?
So when you're feeling down because you've gotten a rejection, remember you're in the game, pat yourself on the back, and write another story.
And so on. That's how you win.
Of course, licking your wounds has its points, especially on the rejects that really hurt. But it's better if you do it as a celebration. So, do what I do when I get one that hurts and treat yourself to a night out and a really silly movie, something guaranteed to make you laugh. The dinner out is the celebration of the lumps and bumps on the road to becoming a professional writer. The movie thing seems to take the worst of the sting away, at least for me. It's hard to laugh and feel punched in the gut at the same time. Not impossible, but hard.
Rejection = you're in the game = you rock!