After a thorough research, there exists the same question that gives the quote:
Germany “would have Paris
for lunch, St. Petersburg for dinner.” ~Kaiser Wilhelm II
The Schlieffen Plan was supposedly for the reason of knocking France out of any war in 6 weeks. And then, once Russia who is the ally of France came to a thought that they have to fight Austria-Hungary and Germany on their own, then and there, they made peace. This made Germany won quickly.
