I had a teacher in high school who picked on me and made me work really hard -- some scrawny, borderline-anorexic kid with no friends who just worked out a lot and didn't eat enough and slept way too much.
He taught English. He got me writing, something I had always enjoyed but never took seriously.
By the end of his class, I had gained some weight. I wasn't working out all the time and I was enjoying eating a bit more again. I was seeing my friends again.
And most of all, I really took a liking to writing and began taking the craft seriously. I owe my passion to him, my career to him -- hell, my life to him. I probably would've wound up in a rehab facility receiving treatment for disordered eating. I never would've written for fun, seriously, found jobs doing it.
I never got to tell him. He killed himself the day or two after the school year ended. Blew his brains out in his car. It was very unexpected and I miss him everyday.