In many ways war and combat are all about calculated risk. Ground combat troops, like the infantry, are masters of controlled chaos, which means they are experts at assessing risk and responding to it appropriately.
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.