For me, there are 3 things:
Joining the Navy. Turned me from a boy into a man.
My amazing cousin passing away at 31. Encouraged me to not be afraid to fail; to chase any opportunity I wanted.
My marriage ending. Caused me to analyse myself intensely, and build the final major aspects of my personality and outlook on life.
And I could possibly add:
Now your turn.
Luck, real friends, the pursuit of knowledge and knowledge itself, art, music, the intense pursuit of worthwhile goals.
Let me also add being in West Berlin, Germany during 1959 - 1962. Being in that threatening Cold War climate taught me to live in the moment. It also changed many of my social and political points of view and allowed me to see my own culture without blinders on. Intellectually, I grew more from that than I did from my entire undergraduate education.
Hope I did this right? Good post!