Survival instinct and evalutation of the risk/benefit factor.
But even on this, everyone is different. I can only speak for myself but I can assure you that my sense of fear, the more primal one, the fight or flight response, has gone to shit completely. I can watch horror movies at night at home alone and not blink an eye even at the jumpscares.
If someone put a gun to my head I'll probably laugh and mock him hoping he pulls the trigger. In other situations, like is someone tried to stab me, I would fight back because the chanche of dying is slim and I'll probably just end up severly injured.