A book quote from Beyond Band of Brothers by Major Dick Winters and Cole C Kingseed.
"Physical exhaustion leads to mental exhaustion, which in turn, causes men to lose discipline. Loss of self-discipline then produces combat fatigue. Self-discipline keeps a soldier doing his job. Without it, he loses his pride and he loses the importance of self-respect in the eyes of his fellow soldiers. It is pride that keeps a soldier going and keeps him in the fight."
"One last observation on combat fatigue: When you see a man break, he usually slams his helmet down and messes up his hair. I don't know if its conscious or unconscious, but a soldier goes to his head and massages his head, shakes it, and then he's gone. You can talk to him all you want, but he cannot hear you. When he reaches that point, the best thing for everybody is just to let him take a walk."