Consider this from Martin Seligman's Learned Optimism: "I believe the traditional wisdom is incomplete. A composer can have all the talent of a Mozart and a passionate desire to succeed, but if he believes he cannot compose music, he will come to nothing. He will not try hard enough. He will give up too soon when the elusive right melody takes too long to materialize. Success requires persistence, the ability to not give up in the face of failure. I believe that ... OPTIMISTIC EXPLANATORY STYLE ... is the key to persistence.
"The explanatory-style theory of success says that in order to choose people for success in a challenging job, you need to select for three characteristics: (1) Aptitude. (2) Motivation. (3) Optimism. All three determine success."
(Seligman's extensive work with Met Life salespeople, among others, proved out the above—in spades.)
(FYI: Pessimist: Good things ... "I'm worthless, but got lucky on this one." Bad things ... "I'm a bozo who deserved my sorry fate."
Optimist: Good things ... "I deserved that; I'm the cat's meow." Bad things ... "I'm the cat's meow, but the cat had an unlucky day; tomorrow will be better for sure."
Seligman's research results demonstrate that the gap between P's and O's really is Grand Canyon.)