I agree, it just happens and you do it. If you think about it, it probably won't happen.
Several years ago I was walking back to my car along the shore of a lake.
I came across 5 big biker types along the shore, 4 of them were beating the shit out of the other one.
His woman was running around crying for them to stop, and they just kept pounding.
They were all obviously drunk.
As I came across them I yelled out "OK, I have no beef with you but you've had your fun. Let me get him out of here."
The guys broke off their attack, and I walked over and helped the victim up off the ground, and help him walk outta there.
I took he and his woman back to town and gave them a place to stay for the night.
Afterwards I was shaking, I'm sure they were thinking of ganging up on me and beaten me to a pulp too.
I guess the element of surprise, plus I was outside their group, they were a bit embarrased to be caught.
But for years later that sticks in my memory as a kind of shining moment I'm glad I experienced.