A little over 20 years ago, my grandfather gave me a small box of his Army Air Corps accoutrements from his time as a World War II bombardier aboard a B-24. I was mystified by it at the time. In fact, I even placed some of his items in a small shadow box and I still display them in my office today.
Benjamin Franklin nailed it when he said, "Fatigue is the best pillow." True story, Benny. There's nothing like pushing your body so far past exhaustion that you'd willingly, even longingly, take a nap on a concrete slab.