It has been a million years since I read anything on the subject. That won't stop me from blathering though!
I had read that the original Schlieffen Plan had taken account of the manpower requirements to reach the coast. However, with increased fears about the needs in the east (ie Russians), the plan was modified for a number of years prior to the war. Primarily by reducing the strength of the right wing in favour of deployment to the east and even strengthening the centre/left in the west. And modified further still once the balloon went up. The result was a German right that did not have enough raw manpower to complete the sweep.
I even think that the far right was to swing west and south of Paris in the original plan.
Needless to say, that is not what happened. In fact, I doubt you can really say that the plan that carries the man's name was even tried given the modifications to it.