Mannerheim roughed up the Soviets pretty badly in the winter war and Hitler had great respect for him. Mannerheim was an aristocrat, spoke different languages, and had the iron cross.
The thing is Mannerheim basically refused Hitler's request for major assistance particularly for army group north at the siege of leningrad. It was clear to Mannerheim and basically everyone that the tides had already turned. He didn't wanna antagonize the Soviets any further except defend Finland while giving marginal assistance to the Germans.
After the battle of Stalingrad, Army group south in the caucusus nearly got entrapped and destroyed had it not been for Manstein's miracle where he performed a tactical withdrawal followed by a counter-offensive.
Whats interesting was what happened after Manstein's miracle. Winter was approaching and a lot of German soldiers went back home briefly for a break before returning the next year to the front for the Battle of kursk. Both sides basically had a lot of time to prepare for the last major showdown. After the Battle of Kursk it was all downhill from there for Nazi Germany. The Soviets could replace their massive tank losses, massive loss of manpower, and they stubbornly defended their positions while counter-attacking whenever they could.
The lesson from this is that if you think you're vastly superior to your enemy and can defeat them quickly, then surely you can be smart enough to ask yourself what if you're wrong.
