Why did the Germans’ plans collapse in 1914-1918?

The German war plan of the 1914 model was created taking into account a quick war, that is, first to defeat France, which they considered a rather weak enemy (based on the experience of the war of 1870-71), and then to fight with Russia in the east, using the factor of its curved border.

In 1915, a plan was created with the intentions of withdrawing Russia from the war, but this did not work out.

In 1916, they again tried to knock France out of the war by storming Verdun, but the attrition tactics did not work.

In 1917, the focus was on defense.

In 1918, despite Russia’s withdrawal from the war, Germany in the west was defeated by the fall.