kimbery, when you attack a country size of russia (or even china) - you better make long term preparation.
Failure to prepare is preparing for Failure.
The only time germans cut through russians like butter is June-July 1941. By August the offense was stopped. The Blitkrieg was over. Germany was done. It was only a matter of time. IN fact, it was only a matter of time for Germany ever since September 1st 1939.