First World War attrition is used to test the idea of wearing an enemy down through repeated battle. The Verdun forts are characterized as intended to consume enemy forces. Keeping such fighting going requires both sides to maintain the supply and replacement effort. The resulting exhaustion therefore reaches the army sustaining the defensive system as well as its opponent.
Notable Point · 32:33-33:18
Why attrition consumes both armies
A Verdun digression explains why an effort to exhaust an enemy also consumes the force sustaining the battle.