One of my favorite quotes comes from Samuel Beckett: Fail Better. When the rejection letters pile up or the task of selling a story seems insurmountable, I always return to this quote.
Because let's face it, in this business you are going to get rejected. This can sink your mood, but don't let it sink your career! Rejection is not the end, it is only a stepping stone to achievement.
There are several ways to overcome the rejection blues. I often find reading other's stories of rejection and success to be particularly motivating. Some sites like Literary Rejections or Bizarre Publishing Stories feature famous authors' struggles to publication. The Write1Sub1 blog and comments left by our participants can be helpful. It's good to know you're not alone in your suffering. And sometimes, the best way to beat the blues is with a cup of coffee, a long walk with your dog, or lamenting with your writing buddies about how much rejection sucks.
However, the old saying holds the truest: When you fall off the horse, get right back on! The best way to overcome rejection is to send that story out again. Keep pushing forward to the next market, the next story. Park your butt in front of your computer and don't leave until the job is done.
Try again, fail again. Fail better.