I came to think of it as a kind of zen practice: the Zen of not fucking up.

War is life multiplied by some number that no one has ever heard of.

Stripped to its essence, combat is a series of quick decisions and rather precise actions carried out in concert with ten or twelve other men. In that sense it’s much more like football than, say, like a gang fight. The unit that choreographs their actions best usually wins. They might take casualties, but they win. That choreography—you lay down fire while I run forward, then I cover you while you move your team up—is so powerful that it can overcome enormous tactical deficits. There is choreography for storming Omaha Beach, for taking out a pillbox bunker, and for surviving an L-shaped ambush at night on the Gatigal. The choreography always requires that each man make decisions based not on what’s best for him, but on what’s best for the group. If everyone does that, most of the group survives. If no one does, most of the group dies. That, in essence, is combat.

The problem is that it's hard to aim a rifle when your heart is pounding, which points to an irony of modern combat: it does extraordinarily violent things to the human body but requires almost dead calm to execute well.

Most firefights go by so fast that acts of bravery or cowardice are more or less spontaneous. Soldiers might live the rest of their lives regretting a decision that they don’t even remember making; they might receive a medal for doing something that was over before they even knew they were doing it.

The Army might screw you and your girlfriend might dump you and the enemy might kill you, but the shared commitment to safeguard one another’s lives is unnegotiable and only deepens with time. The willingness to die for another person is a form of love that even religions fail to inspire, and the experience of it changes a person profoundly.