On Killing

We assume that for a trained soldier, pulling the trigger is a reflex—a simple, almost mechanical act of will. In the heat of battle, with survival on the line, we believe the human capacity for lethal violence is easily unlocked. We picture a switch being flipped, transforming an ordinary person into a weapon. But what if this core assumption is wrong? What if the most profound, deeply ingrained resistance a soldier faces on the battlefield comes from within? What if the human mind, even when trained and conditioned for combat, possesses a powerful, almost universal inhibition against killing another human being, an inhibition so strong that it causes the majority of combatants throughout history to consciously or unconsciously avoid firing their weapon at an enemy they can see?

This startling possibility is a historical puzzle that haunted military historian and former Army Ranger Dave Grossman. While analyzing combat data from World War II, he stumbled upon a shocking statistic: in many engagements, as few as 15 to 20 percent of riflemen actually fired their weapons. This was a pattern, a psychological barrier that armies had unknowingly struggled against for centuries. Driven to understand this phenomenon, Grossman, a professor of military science, embarked on a journey through history, psychology, and firsthand accounts from veterans. He wanted to uncover the hidden psychological cost of killing and to map how modern military and police training methods have systematically, and perhaps dangerously, dismantled this innate human resistance. The result was On Killing, a work that explores the dark, unexplored territory of what it truly takes to make—and unmake—a killer.

Module 1: The Hidden Resistance to Killing

The central argument of the book is a startling one. Most healthy human beings have a powerful, innate resistance to killing other people. This is a deep psychological barrier, a kind of "safety catch" in the human mind.

For centuries, military leaders missed this crucial insight. They attributed low kill rates to poor training or bad morale. But Grossman presents compelling evidence to the contrary. He builds on the work of U.S. Army Brigadier General S.L.A. Marshall. After World War II, Marshall’s team interviewed thousands of soldiers immediately after combat. His research revealed a shocking statistic. Only 15 to 20 percent of American riflemen in WWII fired their weapons at an exposed enemy soldier. The majority of men on the front lines, while brave in every other way, simply could not bring themselves to kill. They would rescue wounded friends. They would run ammunition through machine-gun fire. But they would not shoot to kill.

This wasn't an isolated finding. Grossman shows this pattern repeats throughout history. In the American Civil War, soldiers armed with highly accurate rifles should have inflicted catastrophic casualties. Yet regiments often killed only one or two men per minute. After the Battle of Gettysburg, an inspection of 27,000 recovered muskets revealed that 90 percent were loaded. Thousands were multiply loaded, with soldiers ramming charge after charge into the barrel without ever firing. They were going through the motions of combat. They were posturing. But they were not killing.

So what's going on here? Grossman suggests this resistance is a fundamental part of our species. In intraspecies conflict, most animals posture, threaten, and display aggression to avoid a lethal fight. Humans are no different. The primary activity in historical combat was posturing. The noise, the smoke, and the chaotic maneuvering of battle created the illusion of violence. But much of it was a non-lethal show. Soldiers would fire over the enemy's heads. They would aim for the sky. They would do anything to avoid the terrible intimacy of taking a human life. This psychological hurdle is so strong that many soldiers, when faced with a direct, personal confrontation, would rather die than kill.