Humanity.
What got you into your self-defense, refusal to be a victim, won't go down without a fight mindset?
I think I was born with it. I don't remember any moment of realization. I never was a small kid or the biggest, but I wasn't afraid to fight anyone else in school (except for the one or two guys that had a substantial criminal record by 7th grade and were known to carry a big knife). The only people that tried to hassle me were the smaller, wise-ass types that knew I had a slow fuse and wasn't going fight with them on account of their size anyway - they were kind of like those fish that stick to the side of a shark for a free ride.
In college, I had a guy come up behind me, say, "hey, what's up?" and punch me in the face when I turned around. I never saw him before and when he realized my couple of teeth less and bloody-faced self was about to stomp his ass he ran like a chicken (a really fast chicken). I'm pretty sure I was a mistaken target of some sort, but it enhanced my understanding that minding your own business won't always keep you out of trouble - sometimes it comes looking for you, and sometimes it's looking for someone else and finds you by accident.
I suspect my occupational direction had something to do with wanting to help others who were victims and to help people prevent themselves from becoming victims.