War in trenches brings two soldiers to fight without even seeing each other. Both of them think the other is their enemy and an awful person, and because of that he must be annihilated. This is what reads the manual which has been given to every soldier. A sortie brings a soldier to take the position which used to belong to the other, and as a consequence he discovers a manual which reads that the awful person, the one to be eliminated is him.
The horrible enemy is no different than him; the soldier understands the idiocy of a pointless war.