This is a gross simplification, by my experience has been that there is also some luck involved in "on the street" confrontations. As a teenager, I lived in an area that was invested with gangs and drugs. In fact, I literally lived next door to a major cocaine/crack dealer who worked for a Mexican cartel and who had a group of police in our [major SoCal, you would instantly recognize the name] city on his payroll. Some of the things I learned by talking with him about how "average street thugs" operate in an organized manner have stuck with me as lessons in vigilance my whole life.
As has been mentioned here, criminals, just like coyotes/hyenas in the wild, target the easiest-looking victims, and rarely confront them head-on. Much more likely is that they will hit you from behind or slash/stab at you quickly from close range with a hidden weapon if they really mean to attack. Working in pairs, one will distract your attention with menacing behavior, but will have no intent to attack; it's the guy he knows is hiding behind you somewhere that will come up and smack you in the back of the head with a blackjack. The luck I mentioned comes in play when something like this happens, and involves whether you are still physically able to get away from the attack, and whether you survive it.
I'm pretty sure there are a few LEO's on this site...they would be a much better resource for information on what goes on with street crime. But I know it's been said here before - if you want to learn effective self-defense, take a self defense class. I took one as a teenager, and they spent very little time on techniques for physically confronting people...they spent most of the time talking about how not to put yourself in a position to be a victim and how to get away from an attacker as quickly as possible if need be. The actual techniques they taught were fast, basic, brutal, and devastating. I've spent my life since hoping that I never have to do anything like that to another human being.
Just my .02...it's a good discussion going here. Thank you all for providing the food for my thoughts.