@matrix in "Storm Of Steel" he cites an experience he had on the front.

Basically, a member of his unit, who was generally a slacker and weakling, who didn't want to do any hard labour, was motivated enough by artillery shells falling all around him to run back and forth from an ammunition pit some distance away, bringing 50kg shells by himself for the guncrews to fire.

As Junger essentially states, war brings out the superhuman qualities of people that they never knew they even had.