Easy,

As Germany did in Poland, Hitler thought that he could invade quickly and grab a chunk of land and get away with it.

Unfortunately for the idiot Putin firstly his army wasn't up to the job and secondly Ukraine was far stronger than it had been in 2014 and stopped his army dead, and finally the resolve of the west to support Ukraine was far beyond what Putin expected.

His army is getting hammered and now they are pushing for peace.