Communism—good in theory, [but] in execution it fails.

"There’s a Sucker Born Every Minute" - attributed to P.T. Barnum.

That is exactly how socialism (and its children: communism, Nazism and fascism) has survived from one generation to the next. Socialism makes grandiose promises that it cannot nor ever intended to keep. Once it has control the people who supported it are trapped by poverty, ignorance and starvation to do anything.