My father, B-17 navigator, said he accepted that he was going to die in combat. The odds at the time of surviving were terrible (about 80% casualties).
He did survive (hence my existence), and told me that whenever he felt down about something he'd remember his buddies who died in the war and how he'd been given a chance to live through it, and he'd re-appreciate his life.
Upon his return to the states, the crews were led to tables to eat. There was nothing to order, the staff assured them "we know what you want." Sure enough, they did - steak, eggs, tomatoes, etc.
Upon return to civilian life, he said he was astounded by the triviality of peoples' everyday life concerns. They were going to live another day, what did they have to be concerned about?