There's a story going around about the subject of why communism doesn't work. The story is most probably apocryphal, but it goes approximately like this:
A university professor gets tired of his progressive students going on and on about the virtues of Marxism and communism, so he decides to put it into practice: He tells them that from that moment forward all test will use communist principles and therefore test results will be distributed among all students equally. In other words, every student will get the average of all test scores. The students agree with this.
Tests are scored on a 0 to 5 scale. When the next test is over, every student gets a 3. The students that did not work hard for the test, and their test got just a 1 or a 0, were happy. The students that worked hard on the test, to get a 5, were upset for only getting a 3 instead.
This caused demotivation in the hard-working students. Why work hard on the next test when they would get a lower score regardless? Even the other students got demotivated because they saw that they didn't really need to do anything to get an acceptable grade. Therefore in the next test the average result was a 1, which every student got.
This caused even more demotivation because those who still worked even moderately hard on the test were given a much lower score than they worked for. Thus in the third test every single student got a 0, ie. every single student failed the test. Even those that got an actual grade above 0 in that test.
True or not, I think this story demonstrates quite well why absolute communism does not work: It demotivates people. Why work hard, when you get no benefit from your efforts? Why work hard, when everything is given to you regardless of what you do? And when this demotivation spreads among the entire population, everybody fails. Everybody loses.