Much of the book is an investigation into the nature of courage. O'Brien quotes philosophy and poetry, observes various officers, and examines his own pre-Vietnam heroes for clues to the nature of courage. However, it is not an abstract question. It matters because O'Brien wants to conduct himself honorably in the war. He is aware that soldiers lacking courage can do terrible things. During one firefight, O'Brien finds himself "writh[ing] in a meadow," terrified (135). It is not shame that concerns him; rather, he sees a connection between the lack of courage and the commission of war crimes. A cowardly soldier is a dangerous soldier: "If a man can squirm in a meadow, he can shoot children. Neither are examples of courage" (135). As much as O'Brien fears dying, he also does not want to leave Vietnam as a war criminal.

Two main definitions of courage emerge, both of them drawn from works of philosophy by Plato. The first is the idea that courage is "wise endurance" (137). This phrase comes from Plato's philosophical dialogue Laches, in which Laches and Socrates agree that surviving is courageous, but that it also matters how you survive. Only if one knows what they’re doing can their actions be counted as courageous.