Mark--hope your knee is getting better. Re:Martial arts, I have dabbled in a number, but in sparring in any of them , something I learned from my college boxing coach has always stuck with me. "Don't worry about how big or tough they look. 99 percent of people really don't want to hit other humans. Worry about the 1 percent that will actually hit you and mean it". Assuming there is some truth in that (it has been my experience that it is true)--can this be trained? In other words--do self defense courses work to take you out of 99 percent and be in the 1 percent--at least when it matters? Or are you stuck with what you are born with--to paraphrase Popeye--"you am what you am".
And I guess secondarily--do you think it is nature or nurture-or if both is one primary?
Deepish thoughts.