J.K. Rowling (Harry Potter's author) about the importance of failure in her Commencement Address at Harvard:

"What I feared most for myself at your age was not poverty, but failure. (...) Now, I am not going to stand here and tell you that failure is fun. (...) So why do I talk about the benefits of failure? Simply because failure meant a stripping away of the inessential. (...) Failure gave me an inner security that I had never attained by passing examinations. Failure taught me things about myself that I could have learned no other way. (...) The knowledge that you have emerged wiser and stronger from setbacks means that you are, ever after, secure in your ability to survive. You will never truly know yourself, or the strength of your relationships, until both have been tested by adversity."

There are also some great parts about to confront oneself to others and other cultures ("How much more are you, Harvard graduates of 2008, likely to touch other people’s lives?). Why do I blog this? collecting resources about failures for a book project.