I actually think this is one of the more realistic aspects of this excellent short story, as we see the true human psychological cost of war in the face of the sniper. The story presents us with the student, whose "eyes had the cold gleam of the fanatic." His experience of war and the effect that this has had on him is self-evident, as we follow how he manages to outwit his unknown and anonymous enemy on the opposite roof and kill him, descending from his perch victorious. However, I think it is perfectly realistic that having assumed this cold and calculating character which was necessary to ensure his survival, that when he is victorious, he is able to relax and suddenly can comprehend the enormity of what he has done in the following passage:
The sniper looked at his enemy falling and he shuddered. The lust of battle died in him. He became bitten by remorse. The sweat stood out in beads on his forehead. Weakened by hsi wound and the long summer day of fasting and watching on teh roof, he revolted from the sight of the shattered mass of his dead enemy. His teeth chattered, he began to gibber to himself, cursing the war, cursing himself, cursing everybody.
He is only now able to show and demonstrate the human, sensitive side of his character after having to rigidly maintain his cold, calculating character to ensure his survival. This story shows that fighters do have a human, sensitive side, but they must keep it very strictly under lock and key. Even then, it is able to break out.