More specifically, the ability to fail well. To shrug off your failure and come back just as hard as the first time. It's what makes champion sportsmen, successful inventors and industrialists and every career artist/writer/actor/dancer/musician/creative type you'll ever meet.
Thing is, that's harder than it sounds. Failure is hard on the ego, and failing at something you really, deeply care about can be devastating.
Or not. Thomas Edison failed something like 3000 times before he got a light bulb to work. Walt Disney was turned down by over 100 banks before he was able to finance his first amusement park. Actors get turned down at one heck of a lot of auditions for every part they get, and there isn't a writer alive, no matter how bestselling, without a fair-sized stack of rejection letters behind them.
Failure is how we succeed, *if* we don't let it get the best of us. And how do we do that? How do we take those rejections, those hard knocks, and come right back swinging?
The key is how we explain our failures to ourselves.
The ones who stay down when they fall, or need MUCH more time to get back up, are those who see their failures as Pervasive, Powerful and Permanent. For example, Joe Writer gets a rejection letter. He thinks, "I suck at everything (Pervasive), this letter proves it (Powerful). I'll *never* be any good as a writer (Permanent)." It takes him a week to work up the nerve to send the next submission, if he doesn't just stick his manuscript in a drawer and give up. After all, he's no good, right?
Those who bounce back do it first in their heads. The better they see their failures as Isolated, Weak and Temporary, the better they do on their next performance. Jane Scribbler gets her rejection letter too, but she is able to think, "It's only one letter (Isolated), and just one market (Weak). Somebody's bound to say 'yes'."
I know, this perspective is easier to say than to do, especially when your latest setback has you feeling like you've been kicked in the guts. But, if you want to succeed, learning to fail well is vital.
One side point: Denial, Distortion and Projection are also effective ways to deal with failure. Effective, but not exactly healthy. Refusing to allow that failure into your mental landscape (Denial), reshaping reality to meet our mental needs (Distortion) and pushing the causes of our failures outside ourselves (Projection-- often persecutory in nature), these are elemental ways our ego protects itself from damaging information.
Thing is, what protects our ego often blights our character. Blocking failure robs us of the opportunity to correct the causes of our failure and eventually succeed. Nothing good can come of this...