Four elements make up the climate of war: danger, exertion, uncertainty and chance. Courage, above all things, is the first quality of a warrior.

—Carl von Clausewitz, On War

Every battle in world history may be different from every other battle, but they must have something in common …. the behavior of men struggling to reconcile their instinct of self-preservation, their sense of honor, and the achievement of some aim over which other men are ready to kill them. The study of battle is therefore always a study of fear and usually courage, usually also faith and sometimes vision

—Sir Herbert Butterfield,

Never, never, never believe any war will be smooth and easy, or that anyone who embarks on this strange voyage can measure the tides and hurricanes he will encounter.

—Winston Churchill

The field of battle is a field of adversity. Man is at odds with the environment as he tries to come to grips with the enemy. Exposure to harsh physical conditions—fatigue, heat, cold, hunger sap the strength and wears at the resolve of the warrior. Physical conditions, however, are not the only, or even the greatest, challenge to overcome. The uncertainty inherent on the battlefield—uncertainty of one’s own forces, the enemy, and the environment affects the judgment of the warrior, inhibiting clear thinking and detached analysis, possibly even paralyzing the decision-maker. The disorder and chaos of a battlefield challenge one’s ability to process events and sort out what is really happening. Time marches on relentlessly, and there’s no way to take a time out. The exhaustion, disorder, chaos, and uncertainty feed the kernel of fear that may range from a healthy respect for the unknown to a gripping terror that leads one to flee in horror.