I take a self-defense/martial arts class several times a week. The biggest thing I have learned is just how difficult it is to defend yourself. If you are caught off-guard or by multiple attackers, it can become nearly impossible to fight back unless you have trained for it.

Being victimized can shatter one's assumptions about the safety, security, and predictability of the world. I found that training in self-defense has slowly returned these to me to a small degree. I don't ever want to use these techniques, but I hope I could if I had to.