How Much Of Success Is Mental?

Derrick Rose went off for a career 50 points, his team mobbed him and NBA players from around the league loved it.

Clay Travis says that because  of all his injuries over the years that Derrick Rose is a good test case  for how powerful the mind is. Rose still has the talent to score 50,  but how much of his struggles were caused by not believing he could  still play at a high level after so much time on the mend?