German Barbarossa attack prior Stalin's Planned Invasion(Cover Map) of Europe Operation ThunderStorm

The Germans, writes Suvorov, enjoyed the temporary advantage of surprise because they were able to position and launch their strike forces just two weeks before the Red Army was scheduled to attack, catching it completely off balance. The surprise was all the greater because Stalin did not believe the Germans would dare open a second front in the East while still engaged against the British. Also contributing to the spectacular initial German successes was the daring and professionalism of the German soldier.
As Suvorov writes:
The [Soviet] defeat at the outbreak of the war [June-September 1941] was due to the fact that the German Wehrmacht launched its surprise attack at just the moment when the Soviet artillery was being moved to the border, and together with it the corresponding supplies of munitions. The artillery was not prepared to deal with a defensive war, and on June 22 was not able to go on the offensive.

Because Germany lacked the natural resources to sustain a protracted war, Hitler could prevail only by completely subduing Russia within four months -- that is, before the onset of winter. In this he failed. During the summer and fall of 1941 Hitler shattered, but did not destroy the Soviet military machine. (As it was, the Germans were able to achieve stunning initial successes only by utilizing Soviet stores captured during those first few months.)
https://www.ihr.org/jhr/v16/v16n6p28_Michaels.html