I will not fight back if I feel I have a means of escape from the immediate threat. That means I won't fight if I feel I can run away, comply with demands, or otherwise defuse the situation without violence.
I have no aversion to violence, I'm not against it on philosophical or any other grounds; I just believe that 'self-defense' means just that; defense of self. Violence means additional risk. I'll take that risk when my common sense tells me it is less risk that to not fight back.
I will not fight to support my ego, to prove a point, or on 'general principles'. My self-defense philosophy is simple; life means more than ego, emotions, or even honor. I will do whatever I believe necessary to survive, including giving up my wallet, watch, cell phone, or whatever. When I do not believe that I can avoid being assaulted, injured, or killed, I will engage in violence with all my ability and strength and I will not stop until I feel the threat is ended.