Why does socialism not work?
Socialism doesn't work because an elite does not like to give up their privileges easily. After it took a wave of bourgeous revolution over a number of centuries to force the aristocracy to give up their powers and to enter a power-sharing agreement with the bourgeois which led to the decline of feudalism. 

Marx suggested that this movement would not stop with the bourgeois, but would then go on to animate the so called third estate.  This indeed did occur over the 20C, but in the final analysis, not successfully and this has led to some people to say that Socialism does not work. The other side of this thesis is that it was simply strangled at birth, and this is what the Trumans policy of containment amounted to.