I think it's the training you receive. You might take it for granted until the first time you actually get into those situations and bullets are flying, but I certainly found that when you do get into those hard situations--and I've been in a few myself--the training did kick in pretty automatically. Sometimes it's almost surreal. You see yourself doing exactly what you were trained to do throughout years of infantry training and company commander training and CO training. You see yourself doing it by the book, as if you're being evaluated.
I think the other aspect, though, that's ingrained into us as a culture in the Canadian Forces and in the army is this concept of leadership from the front and achieving your mission. I always found that when you did have dark hours, and I certainly had a degree of very close personal loss over there, you knew you still had 1,200 soldiers looking at your every move. In the end, your duty was to keep that ship on track and accomplish the next objective or the mission that you had been assigned. I think you get a lot of personal strength from that, and that does get you through from one bad day to the next.