A while ago I read John Keegan's The First World War, in which he goes into great detail on Schlieffen's 1905 "Great Memorandum". Keegan's text implies, to me at least, that the Great Memorandum outlined a supremely-detailed plan of operations for the rapid defeat of France, down to the bridges to be crossed and the roads to be followed, but one that couldn't have worked: according to Keegan, Schlieffen knew that Belgium and France's road network wasn't extensive enough to deploy the huge number of troops he needed to defeat France, and that he literally made the divisions required magically appear at the decisive point on his maps. Nevertheless, the plan was approved for use out of a collective obsession among the German General Staff to rapidly defeat France before turning on the Russian Steamroller inexorably closing on East Prussia.
How accurate is this? I am told that recent research has discredited the notion that there actually was a Schlieffen Plan to defeat France and more of a series of deployment plans to which were appended recommendations to commanders for operations, but I have had difficulty finding anything that might reconcile this with Keegan's thesis, if it can be reconciled at all. Enlighten me, /r/AskHistorians!
I'm not an expert, I only know what I had to do on a bit of work over a year ago, but I remember getting a good mark on it:
Well the Schlieffen Plan relied on 5 huge assumptions in order to be successful:
Invading Belgium would cause no issue with the UK, or France.
Belgium would not resist, or be unable to delay, German invasion
Paris would be captured in a matter of days
Without France, the UK would sue for peace, if they even got involved
Russia would take at least 6 weeks to mobilise troops en masse, and could not stand against Germany
Basically the entire thing just seemed like it would be more accurate if it were a tactic of pre-Industrial Revolution era (though Germany was a relatively recently industrialised nation). Germany had great military minds in command, so the idea they'd rely on such a plan seems disingenuous, there were probably similar plans, and that a best case scenario would play out similar to the Schlieffen Plan, but I doubt this was what they were expecting.
Bear in mind, the Schlieffen Plan is not the plan that was shown in WWI anyway. The Schlieffen Plan is actually a collection separate war plans. One for a simple Franco-German war, one for Entente v Germany focused in the West, one Russo-German war, and another Entente-German war. Then both of the Entente plans were plans within plans, based on the participation (or lack thereof) of the UK and other European nations. So your reading of a "Schlieffen Plan" not truly existing are pretty accurate. The final war plans were a bit of a combination of plans, also from what I understand, the plans were not all that detailed.
Ignoring the practical limitations of getting the German forces through to Paris, which could be possible, just not in the timeframe dictated, but the plan failed on a political level with the invasion of Belgium, which is typical of Wilhelm's Germany and his fundamental misunderstanding of the Great Powers and their interactions.
Here's a couple readings:
Inventing the Schlieffen Plan: German War Planning, 1871–1914 (Zuber)
1914-1918: the History of the First World War (Stevenson)
Also, my favourite Reddit post, a huge repository of free ebooks: