On paper, Russia has significant military advantage. But if you look at the humans doing the fighting, I think you might see some very different levels of commitment and motivation.
The Ukrainian troops are defending their homes. They are up against a wall, so this is a matter of survival. The Russian troops are fighting for something that likely many of them care nothing about. They are being made to risk their lives (and fight their cousins, so to speak). Not only may they have issues with fighting other similar folks, but they certainly don't _need_ to be risking their lives.
The Ukrainian troops are defending their homes. They are up against a wall, so this is a matter of survival. The Russian troops are fighting for something that likely many of them care nothing about. They are being made to risk their lives (and fight their cousins, so to speak). Not only may they have issues with fighting other similar folks, but they certainly don't _need_ to be risking their lives.