Birth of my son.
Hands down.
I was living life, had a mortgage, car payments, job....in my mind..I was thinking "yup, this is life, I'm living it I know what's going on"......then I'm holding this life in my hands...and my first thought is..."holy fuck I don't know anything about ANYTHING"
Another big one..for me...though not quite that big..but it certainly defined me.
Being handed a Prince: Purple Rain tape...in 1989/90 with the Dream Theater's: When Dream And Day Unite recorded over top of Prince on it. Complete musical and life altering moment.......earth shattering.