At the surprising moment when Ulrich von Gradwitz and Georg Znaeym find themselves looking at each other, they cannot react quickly enough to shoot each other in cold blood because they have been brought up as gentlemen who must have words spoken to each other first.
In that "long, silent moment" that the two enemies look into each other's eyes, there is that hesitation borne of civilization and breeding which prevents the men from shooting each other before the huge branch falls upon them.
...a man who has been brought up under the code of a restraining civilization cannot easily nerve himself to shoot down his neighbor in cold blood and without a word spoken, except for an offense against his hearth and his honour.
Since neither their homes nor their honors have been insulted, Znaeym and von Gradwitz miss their opportunities to rid themselves of the enemy because the great beech tree is struck by lightning and a branch crashes upon them. And, so, each man must console himself with the thoughts of his own men reaching the adversary before the others. So, to bolster their courage the two enemies argue that one group will arrive and then kill the other group. However, as fate would have it, wolves arrive before either group of men.