This Twitter thread explains that Russians actually did not expect any serious resistance https://threadreaderapp.com/thread/1499377671855292423.html

They expected immediate collapse of Ukrainian army because this was what happened in 2014. Well, it did not happen this time because Ukraine had 8 years to prepare and prepare they did.

I was actually slightly surprised that they actually went for Kyiv instead of trying to just take Donbas with all they got there. All the military experts who commented the situation before the invasion told that it would be not realistic to take Ukraine with forces this small.

They thought that they will just go to beat up some women and children without any resistance but they were wrong. Corruption, hubris and stupidity kills in war.

The only reasonable explanation I've heard is that Putin has surrounded himself with all sorts of yes-men and that those yes-men basically told him that most of the people would gladly welcome Russia's forces.

This kinda explains why the first wave of Russian soldiers were naive enough to stop in the city and ask common people for directions to the city center.

Obviously we don't know everything going on in the Kremlin, but it does appear that Putin to some degree believed his own bullshit. The the overwhelming force of the Russian Army would knock aside the Ukrainian forces without too much difficulty; that they would even give up and switch sides. He underestimated Zelensky's ability to rally support, and the extent to which the West was willing to forego access to Russian oil and gas. He assumed China would help him withstand Western sanctions, but so far that remains to be seen. Xie obviously doesn't care about Ukraine, democracy, or any of that stuff. But he isn't going to stick his neck out if he thinks it goes against China's interests.