Every single person is different and the way that they react will be different, unless trained to react a particular way. A person who has never been punched in the face, will not protect their face unless it has been ingrained into them with training, however, the training for that is normally, punching that person in the face. The point is that you have to expose the individual to the situation as best you can, and train them how to react to the situation, through desensitizing their reaction of fear, stress, anxiety, panic, aggression, etc. Everyone reacts differently, everyone has a different emotional response to different situations, so in order to how someone will react, we expose them to it as best we can (simmunition, role playing, scenarios) and than evaluate the persons reactions, discuss the emotional responses, and than work to desensitize them from the emotional aspect, while encoring the desired reaction to the particular situation.
I have seen people have emotional response in simulation training and real world operations, that varied from shut down to unable to move fear to the total other end of over aggressive complete pissed off. You can't possibly train for every situation like this, but you can prepare for many situations by continued exposure to similar situations.
My $.02