The history of warfare has shown many times that overconfidence can kill, and this case of misjudgment killed hundreds of thousands. If anyone had a reason to be confident in 1941, it was the Nazis and Adolf Hitler. In 1939, Germany had overrun Poland in a matter of a few weeks. In 1940, France fell in just over a month. Not only did the Blitzkrieg ensure victory, but it seemed to guarantee a quick one as well. Then came Operation Barbarossa, the German invasion of Russia. Attacking Russia, they bet everything. The consequences of failure, even failing to win a quick victory, are shown by history. But in 1941, Hitler considered himself a military genius and, so far, appeared to have lived up to the claim. All of Europe, from Poland to the Pyrenees, was occupied by Germany or was her ally. On June 22, 3 million German and allied soldiers attacked Russia. Somehow, mostly because Stalin refused to believe it was going to happen and executed those who disagreed, the Wehrmacht achieved surprise.
In the first months of the invasion, hundreds of thousands of Russian soldiers were captured. In one case alone nearly 700,000 men surrendered or were killed when a large part of Ukraine was surrounded. Then it began to get cold, and a mistake that is very uncharacteristic of the meticulous planning normally attributed to the German general staff became apparent. The mistake was that Hitler and others were so confident of a fast victory, such as had occurred in Poland and France, that there had been no provision for equipping the army to continue fighting in the cold Russian winter.
Now, this means much more than a lack of overcoats and long underwear. Trucks and tanks were not winterized. The radiators would freeze up and even the diesel fuel took on a wax-like consistency in the subzero temperatures. Weapons froze solid in the middle of a battle and water-cooled machine guns became useless. On a personal side, there were no sleeping bags or insulated tents, so thousands of German soldiers literally froze to death in their sleep.
As quoted earlier, there is an old axiom that no battle plan survives contact with the enemy, but winter can be predicted. Through overconfidence or mistaking the open reaches of Russia for being similar to densely populated western Europe, no provision was made to keep the Wehrmacht fighting in cold weather. There were other factors that led to defeats, such as changing objectives and Hitler shifting panzer divisions around, creating delay. But the real mistake was not expecting another quick victory, but rather preparing for the invasion only under the assumption that all of Russia could be conquered in the few months before the notoriously fierce Russian winter arrived. That overconfident oversight meant that the German army could not fight at anywhere near its best level in the cold weather. It also cost the Wehrmacht tens of thousands of unnecessary casualties from frostbite or worse. Making the mistake of preparing only for the best of outcomes pretty much guaranteed the worst. If the German army had been properly equipped and prepared to continue fighting during the cold weather, they might well have captured Moscow and forced Russia to seek peace on Hitler’s terms.