We are making an assumption that Putin really wanted to 'take' all of Ukraine. If the country does not want you, occupation is expensive and possibly not worth it, USSR found that out and maybe Putin learned that lesson. Maybe he just wanted Donbas and Crimea and to bitch slap all the Ukrainian militia on the border with an attempt to end the 8 years of shelling that have been going on at the border.
The Germans knew they were losing the war because their victories kept getting closer and closer to Berlin.
Russia is getting "curbstomped by Ukraine" but they keep taking territory and towns
We are making an assumption that Putin really wanted to 'take' all of Ukraine. If the country does not want you, occupation is expensive and possibly not worth it, USSR found that out and maybe Putin learned that lesson. Maybe he just wanted Donbas and Crimea and to bitch slap all the Ukrainian militia on the border with an attempt to end the 8 years of shelling that have been going on at the border.