Interesting:

Marshall was a U.S. Army historian in the Pacific theater during World War II and later became the official U.S. historian of the European theater of operations. He had a team of historians working for him, and they based their findings on individual and mass interviews with thousands of soldiers in more than 400 infantry companies immediately after they had been in close combat with German or Japanese troops. The results were consistently the same: Only 15 to 20 percent of the American riflemen in combat during World War II would fire at the enemy. Those who would not fire did not run or hideâ€”in many cases they were willing to risk greater danger to rescue comrades, get ammunition, or run messages. They simply would not fire their weapons at the enemy, even when faced with repeated waves of banzai charges.

Why did these men fail to fire? As a historian, psychologist, and soldier, I examined this question and studied the process of killing in combat. I have realized that there was one major factor missing from the common understanding of this process, a factor that answers this question and more: the simple and demonstrable fact that there is, within most men and women, an intense resistance to killing other people. A resistance so strong that, in many circumstances, soldiers on the battlefield will die before they can overcome it.