I think it was Marshal Davout who said, "Too far." It was such a disaster almost from start (way too late in the year) to the finish.
Marching into Russia, a great many men died of sickness, thirst and exposure. The steppe is something no one anticipated and the late summer/early autumn conditions were almost like a desert. Many horses were lost as well, cavalry had no mounts and there was no proper way to be re fitted.
They outran their supply system (such as it was) and they almost immediately ceased to be an army on entering Moscow. They were a mob that over ran the city and command was not up to controlling the men.
Needless to say they began their retreat in the worst possible condition and it never improved.