Martial arts don't prepare you to defend against real-world violence.

So says Sam Harris, explaining how to deal with violence.

Excerpt:

Herein lies a crucial distinction between traditional martial arts and realistic self-defense: Most martial artists train for a “fight.” Opponents assume ready stances, just out of each other’s range, and then practice various techniques or spar (engage in controlled fighting). This does not simulate real violence. It doesn’t prepare you to respond effectively to a sudden attack, in which you have been hit before you even knew you were threatened, and it doesn’t teach you to strike preemptively, without telegraphing your moves, once you have determined that an attack is imminent.