I just finished reading War by Sebastian Junger and it seems like one of the main things he is trying to get across is that the guys in a unit put their life on the line for their fellow soldiers, that the life of the guy next to you is just as important as your own. The brotherhood that happens in combat can’t be recreated anywhere else and it’s because of this that readjustment into civilian life is so difficult. Survival depends a lot on the ability to compartmentalize. After one battle where three men were killed, a sergeant says, “I wantcha to mourn, and then I wantcha to get over it”.
One of the soldiers that Junger writes about, Brendan O'Byrne, says (on his own website) that 1000 years ago, even 200 years ago, after a war had ended, soldiers had to walk home. During that time they talked to each other, they had a running re-cap of everything they had been through that sort of helped them process everything. Now, he says, they can be in combat one day and in their hometown grocery store the next.