Perhaps this is stupid but I’ve had a number of thoughts lately and thought I should write them down.
The reason that the First World War lasted so long was not the generals or the other classic reasons. The problem was the German Army. If the Germans had not been as determined to win the war on their terms and the German Army had not been so capable, then the war would not have been as long nor as terrible.
The other thought that struck me was that the volunteer and conscript infantry units received very little battle training. Taught to shoot, obey orders, dig etc but nothing of the sort we routinely expect today. Perhaps the obvious aspect of this conclusion is to recognize that the experience of the war was central to the creation of modern infantry tactics.
It is probable that these tactics did not enter their definitive form until the Reichswehr work on formalizing the lessons of the war.