Have read a bit about this subject and there is quite a bit of discussion about the decision by the Germans to pour resources into armor production over the development of long range heavy bombers, this decision also steered resources away from the German Navy as well, but the Germans had gamed Operation Sea Lion came to similar conclusions the US did when it came to invading Japan, there would be massive casualties, and it would require tons of resources. The British still had a substantial home fleet and it would be almost impossible to provide support for landing ships.

There was also the miscalculation during the Battle of Britan where they went away from attacking air bases, which was very successful early, to bombing cities.

However, the decision that impacted the Moscow campaign the most was likely the attempts made to secure oil fields in the Caucuses, early on there was a realization of the need to secure oil sources.

This is a very practical answer, but if war was just about the numbers France would not have fallen in a month.