War is an extreme human activity—not only because of the horror of war, but because of the severe emotional, physical, psychological, and moral strain it has on its combatants. Understanding war from the combatant’s point of view is hard enough without personally experiencing war. Without the direct experience of combat, an epistemic gap lies between one who knows what it is like and those lucky enough not to experience it. Consequently, the theoretical propositions of just and unjust conduct in war become difficult to support. I argue that just war theory and its tenets such as jus in bello, or just conduct in war, needs a thorough examination of combat experiences to define the principle with the reality of war in mind. For example, as a precept of moral responsibility in war, jus in bello is an abstract principle which can be supported by concrete historical examples if and only if the epistemic gap between the experience of combat and abstraction is bridged by a consideration of the reality of war.