Russia's underestimation of Ukraine led to significant failure, UK says

The British defense ministry in an intelligence report said “Russia's underestimation of Ukrainian resistance and its best-case scenario planning have led to demonstrable operational failings.” 

Those failings prevented President Putin from announcing significant military success in Ukraine at the 09 May Victory Day parade.

“Russia’s invasion plan is highly likely to have been based on the mistaken assumption that it would encounter limited resistance and would be able to encircle and bypass population centers rapidly,” the MoD said in a tweet.