I think it's pretty hard to know for sure til you're in a survival situation. Sometimes the folks that seem weak (eg very small children, frail elderly people with serious medical conditions, etc) will survive things that are really horrible while young and fit people perish. Likewise there are cases where very small and weak individuals have performed stunning feats of strength while under stress. Some of the guys that talk big on gun forums about how they "dial 1911, not 911" freeze up when confronted and ten year olds savagely drive off kidnappers.

There are lines I have no intention of every crossing but who knows what I might be capable of if my back is against the wall.