The best thing about rejections is that they ensure no one who's not excited and passionate about your work will be in charge of selling it. The only thing worse than no agent is a BAD agent! (or should I say, and agent who isn't your #1 fan!). Same thing with editors!
When we get rejections from a pool of agents or editors, they are actually helping us by weeding out the ones who aren't a good fit for our books. And don't we deserve someone who loves our books? I say, let 'em go! It wouldn't have worked out well anyway if they weren't the right person in the first place. :)
That said, when I sent my second-written novel out for submission to an agent and to Harlequin, I got form rejections from both (this was 2000). I was so completely wounded and emotionally hurt from those rejections that I didn't grow my imaginary balls back for another ten years (when I started submitting again in 2010).
By sending out your work, getting rejections but continuing to go for it, you're already ahead of the game by a long shot. We've never even heard of all of the writers who just give up completely in the face of rejection, as I had done for so long. The ones we do hear about, however, are the authors who just keep on keepin' on. They put the rejections behind them and keep submitting and writing new books.
I always know someone's closer to getting published when the amount of rejections starts picking up -- it means they're really in the game!
Oh, and as a side note, if you are an already-published author, and you found this post because you've gotten a rejection letter despite not being a newbie anymore, I am here to tell you that even published authors get rejections. We're just shielded from them by our agents. I remember in 2011 getting a rejection (and I'd been published since 2010), but when I looked online to see if any published author in the history of the world had every been rejected before, I decided by the lack of evidence, that I was the ONLY one!!