“Socialism cannot possibly do what it promises.”
Because socialism is based on the “fatal conceit” that one man or one group, one official or a team of central planners with a master degree from Harvard (or Yale, or LSE, or la Sorbonne) can gather all the information needed (and understand it!) in order to transform the world (that includes reshaping human nature) according to their believes or ideas.
They don’t trust your wishes, your intellect, your abilities, your desires. They want to rule your life by designing an economic system that replaces the spontaneous order of the marketplace by their own wishes, desires and ideas of how things “should be”.
NOTE: If you want to understand more about the subject, please read “THE FATAL CONCEIT”, by Friedrich von Hayek.