The weird job of acting is that it is so simple. You just see the person in the situation. It is whatever you have to do to get there. Some people want to stay up all night or cut their toe off. For me it is a bunch of reading, and hanging out with real people, I do that. You never know what you are going to get. It might be the shoes people wear.
Just think of the trust that often exists in soldiers. Within their own unit, you could say they have to trust each other. A spirit of camaraderie builds up and, in the end, they will risk their lives for each other. They may even go so far as to dehumanise the other, enemy group - a mechanism you can also observe in chimps.