There is an old and true saying, train hard, fight easy, but having said that a lot of comments on this thread re be aware, dont let yourself get into situations where you have to fight make a lot of sense
I try to stay out of situations that might make SD necessary but in the one incicident that I had to use it, I was able to restrain the other guy (a good kid until he got high and stupid,) and all he got for his trouble was scrape on his neck from my watch band and an injured pride, which he got over a couple of days later.
I've had instructors and masters tell me that the there's nothing wrong with just walking away rather than fight. If you can do that, you've still won.
Nope... never failed me. In fact, in reflection, it has surprised me how well it did work without having to think about it. I really don't go looking for a fight, so when it happens, I am not the aggressor and I have always walked away from it. The other guy wasn't always beat to a pulp, but he got the idea in pretty short order that he might want to pursue his thuggish intentions with a less capable target. I love to embarass a bully in front of his friends.
True about knowing when to keep your mouth shut too. Good point. Too many vocal friends and it is just best to remove yourself from the situation all together.