How did German intelligence underestimate Soviet military reserves?

German intelligence significantly underestimated the Red Army by failing to account for the vast depth of Soviet military reserves available to Joseph Stalin.1

While German planners correctly identified approximately 150 Soviet divisions stationed in the western regions of the U.S.S.R. and estimated that an additional 50 could be mobilized, they fundamentally miscalculated the total capacity of the Soviet state. In reality, the Soviet Union deployed more than 200 fresh divisions by mid-August, bringing their total strength to 360 divisions.1

This intelligence failure meant that even after the German forces successfully shattered the initial Soviet armies through superior military technique, they were repeatedly confronted by new, fresh units. This miscalculation was compounded by political assumptions that the Soviet regime would collapse within months due to a lack of domestic support, as well as internal German command disputes that wasted critical time during the summer of 1941.1