Lenin’s biggest mistake was thinking this whole “dictatorship of the proletariat” phase was going to be this magical normal period that no human would abuse ever, completely ignoring millennia of human history, human behavior, and the dynamics of power that would make that sort of thing literally impossible. Not only does absolute power corrupts absolutely, but even if a leader was immune to such corruption, dictatorships are never propped up by one single leader. They are precariously installed by groups of people who have other units of power, like the military, to keep the system in place.
One of those powerful people can simply say: “Keep this dictatorship in place or I will torture you and your entire family while spreading propaganda about detestable crimes, until eventually I’ll feed you to the angry mob and prop up a new dictator.”
And that’s it. The real communism dream never happens. Corruption quickly floods the state, and wealth disparity continues unchallenged and unabated. It’s just more hidden, under the guise of a system of equalative poverty for one class of people and gradients of power for another class of people.
Hell, this even happens with failed democracies, like Russia. Everybody gets behind the new system, but without the right kinds of checks and balances, corruption invades and, eventually, it’s a democracy in name only. But, at least democracy never had any notion of a dictatorship built into the philosophy. Democracies are still really hard to keep in place, but communism is a doomed idea from the very start.