In Marine Corps boot camp recruits learn two things very quickly. The first: If a drill instructor looks happy, you’re fucked. Second: These guys go ape-shit for cadence.
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.
And no one knows that better than military service members and we have the pictures to prove it.