It goes further than that. In order for Socialism to work perpetually--
Let me digress there for a moment: Socialism that confiscates wealth and does no more will eventually run out of money. That's been true everywhere it's tried.
--perpetually, it requires that people be altruistic. That is, those who can do, will do, and willingly give away the fruits of that labor to those that cannot or will not do whatever it is to generate wealth in society. That is, the rich will willingly become equally poor but still work just as hard at whatever they do to generate the income that made them rich.
Of course, that goes entirely against human nature so the only way it can happen is by force of government. The usual result is a socialist society quickly devolves to the lowest common denominator with the exception of those willing to work outside of the government system. This results in everyone being equally poor except those that move into black market operations outside of the government system.
In a socialist society the economy quickly becomes corrupt, criminal, and predatory. Those without a means to move into the black market become the new poor while those that succeed in the black market become rich.