The Zen masters have the right idea-no pain no gain: thwack a silly nebbish and he'll remember it far longer and more indelibly than any words you muster at him. Not absolutely everything can or should have to be explained, and particularly not to everybody. But a concussion is a value-judgment anyone gets the point of.
I do about 90 percent of my own stunts, and the things I can't do for insurance reasons, like swinging out of a flying helicopter, I wouldn't want to do anyway.