…When the fight option is utilized [among animals of the same species], it is almost never to the death. Konrad Lorenz pointed out that piranhas and rattlesnakes will bite anything and everything, but among themselves piranhas fight with raps of their tails, and rattlesnakes wrestle.
When a man is frightened, he literally stops thinking with his forebrain (that is, with the mind of a human being) and begins to think with the midbrain (that is, with the portion of his brain that is essentially indistinguishable from that of an animal), and in the mind of an animal it is the one who makes the loudest noise or puffs himself up the largest who will win.
Prior to World War II it had always been assumed that the average soldier would kill in combat simply because his country and his leaders had told him to do so and because it was essential to defend his own life and the lives of his friends. When the point came that he didn’t kill, it was assumed that he panicked and ran.
During World War II U.S. Army Brigadier General S. L. A. Marshall asked these average soldiers what it was that they did in battle. His singularly unexpected discovery was that, of every hundred men along the line of fire during the period of an encounter, an average of only 15 to 20 “would take any part with their weapons.” This was consistently true “whether the action was spread over a day, or two days or three.”
[…] General Crook’s men fired 25,000 rounds at Rosebud Creek on June 16, 1876, causing 99 casualties among the Indians, or 252 rounds per hit. And in the French defense from fortified positions during the Battle of Wissembourg, in 1870, the French, shooting at German soldiers advancing across open fields, fired 48,000 rounds to hit 404 Germans, for a hit ratio of 1 hit per 119 rounds fired. (And some, or possibly even the majority, of the casualties had to have been from artillery fire, which makes the French killing rate even more remarkable.)
Lieutenant George Roupell encountered this same phenomenon while commanding a British platoon in World War I. He stated that the only way he could stop his men from firing into the air was to draw his sword and walk down the trench, “beating the men on the backside and, as I got their attention, telling them to fire low.” And the trend can be found in the firefights of Vietnam, when more than fifty thousand bullets were fired for every enemy soldier killed. “One of the things that amazed me,” stated Douglas Graham, a medic with the First Marine Division in Vietnam, who had to crawl out under enemy and friendly fire to aid wounded soldiers, “is how many bullets can be fired during a firefight without anyone getting hurt.”
The weak link between the killing potential and the killing capability of these units was the soldier. The simple fact is that when faced with a living, breathing opponent instead of a target, a significant majority of the soldiers revert to a posturing mode in which they fire over their enemy’s heads.
Indeed, the history of warfare can be seen as a history of increasingly more effective mechanisms for enabling and conditioning men to overcome their innate resistance to killing their fellow human beings.
From On Killing: The Psychological Cost of Learning to Kill in War and Society, Dave Grossman, 1996