Ukrainians can take heart from the history of Finland. Tiny Finland fought the mighty Soviet Union to a standstill. They bloodied the Russians so badly that the Russians left, licking their wounds, running with their tails between their legs. Finland is still free and still keeps the bear at bay. It is the power of courage.
Taking a country is one thing. Being able to stay long-term against organized resistance of a pissed off people, is something else. The Russians should have figured that out in Afghanistan. The Ukrainians have had a national identity since before the Russian Revolution, Ukrainians are not "Russians" as Putin would have us believe.
I wonder how the Russian people feel about the situation, not that they could say... Russians are not bad people. They would prefer peace and prosperity over war. The Russian people just have a hard time keeping the crooks out of Moscow. The Russian people rose up and replaced their government in 1917, maybe it is time to try again.