Yes. There was an interesting psychological study I read about from WWII as a student that basically looked at people's behaviour during war and found that the idea of killing is so stressful that most regular people/conscripts will avoid it at all costs. They will deliberately miss shooting the enemy soldiers, make noise to alert them and things like that. It is only so long that one can survive like that in a military situation - one might see the mind breaking down very easily when confronted with the dissonance of the situation.