IDK about that. Complacency is not good either.
USSR was ascendant in the 1960's and 1970's: won the 1st space race, catching up in strategic arsenals, in Vietnam, had the Mig-21 which smoked its contemporary the F-4, and had unparalleled influence in Africa, Middle East and Latin America. Then in the 1980's alone it crashed down.
Soviets had the weight of 250+ million domestically and another 100 million in Eastbloc, 2nd largest economy, largest military. You would have never expected anyone like Gorbachev to get anywhere near power and in the rare event someone did, they'd be severely constrained by momentum. Even if it declined, it would do so slowly, and be tightly managed.
71% of Ukrainians in 1991 voted for keeping the Soviet Union. 81% of Belorussians. 73% of Russians. 94% of Azerbaijanis.
That is a landslide election result in favor of keeping the union yet what happened? As Xi Jinping himself said, nobody in the Soviet system truly defended it when it was under threat. Not just the weight of the system itself but all the protests of the people and the votes in favor of keeping the Union couldn't stop it from breaking up.