They've obviously been trained and set up to be able to resist, precisely because of the possibility of invasion. But the Russians' intelligence should have picked that up. It shouldn't have been a surprise.
It now looks to me as if NATO had far better intelligence on Russia's plans than Russia did regarding the condition of Ukraine's forces.
You can't blame Ukraine for being prepared. But you can blame Russia for being duped. Looks very sloppy for a major military force.
There are two main problems with the Russian invasion -
Firstly, the war is not in the hearts and minds of the Russian troops. They have no real cause contrary to the Ukranians.
Secondly, there is major corruption in the Russian military whereby a lot of the defence budget is embezzled.
You can read more about that here -
https://sites.tufts.edu/wpf/files/2018/05/Russian-Defense-Corruption-Report-Beliakova-Perlo-Freeman-20180502-final.pdfPutin also miscalculated, believing the Russian speaking Ukrainians in the east would welcome his troops like they did in Crimea. Lets face it, he lives in a palace surrounded by yes men and has very little political opposition to criticise him and give him a reality check. Plus he is 70 years old now and is probably suffering from cognitive decline.