In his most recent "Leadership Wired," John Maxwell wrote about "defining moments." It's a great read and you can click her to view it: http://bit.ly/ppOn73.
I would also strongly suggest that you sign up for the Leadership Wired Email as well -- always great stuff. You can sign up for the email by clicking here: http://bit.ly/mP4Wn6
Here are some quotes from Leadership Wired in regard to defining moments:
"There comes a special moment in everyone's life, a moment for which that person was born. That special opportunity, when he seizes it, will fulfill his mission—a mission for which he is uniquely qualified. In that moment he finds greatness. It is his finest hour."
~ Winston Churchill
"The secret of a leader lies in the tests he has faced over the whole course of his life and the habit of action he develops in meeting those tests."
~ Gail Sheehy
"If I had not been in prison, I would not have been able to achieve the most difficult task in life, and that is changing myself."
~ Nelson Mandela
"You gain strength, courage, and confidence by every experience in which you stop to look fear in the face. You are able to say to yourself, `I lived through this horror. I can take the next thing that comes along.' The danger lies in refusing to face the fear, in not daring to come to grips with it."
~ Eleanor Roosevelt