All will break down if in combat long enough

Inevitably, all will break down if in combat long enough. “Long enough” is now defined by physicians and psychiatrists as between 200 and 240 days. As medical observers have reported, “there is no such thing as ‘getting used to combat’…Each moment of combat imposes a strain so great that men will break down in direct relation to the intensity and duration of their experience.”

Paul Fussell, Wartime: Understanding and Behavior in the Second World War. Oxford University Press. 1989, p. 281. Quote found in
“Morale maintenance in World War II US Army ground combat units” by Kevin Kane, details see reference materials page.