Copernicus
Industrial Grade Linguist
I think the problem is more meglomania than stupidity. He thought he could get away with it but he didn't realize how corrupted his system has become.When it comes to dumb. Nobody tops Pootie. He started a war he is not winning. He has made Russia a failing pariah state. Russia's young best and brightest have left Russia. Immigrated to sane nations. The only thing Pootie has excelled at is being history's most successful thief. Russia is well on its way to being a failed third world state. How is Russia going to reverse this rot?
Megalomania and stupidity are not mutually exclusive. Putin knows exactly what corruption is, because he himself is personally corrupt. He got where he is by exploiting that system of corruption, and he hasn't exactly been a crusader for clean government while in office. Quite the opposite. If he didn't realize how corrupted his system had become, then he was at least very stupid on that score. More likely is that he didn't realize how the corruption would undermine the ability of his military to overwhelm Ukraine.