Soldiers are put into high stress environments where they have to work together as a close group. They are constantly under pressure, and many of them come to enjoy the intensity and brotherhood. When they return to civilian life they might feel totally out of place. Here is an interview with Joe Rogan and veteran Jocko Willink where they discuss some of these issues.
Thanks for your reply. I didn't see the video. Maybe it didn't post or I missed it.