Communist economic policy directly resulted in low productivity, material and technology shortages, and insufficient food production and famine. This is not theory. Communism failed in Russia and the rest of the USSR, China, and North Korea. The reason for failure is intrinsic to communism. and it should be self-evident.
Some things I considered to be self-evident are: people care about themselves, their families and friends. They work to improve the lives of this 'inner circle'. Some people might care about strangers too, but usually not at the expense of this inner circle and not when they dislike those strangers and consider them undeserving/freeloaders.
When the results of your work are not funneled to your inner circle but put into a 'common bucket' and split equally, it decreases your motivation to work, especially when you see that people who contribute the bare minimum get to take from the common bucket just as much as you. That creates the incentive to work less because your reward from the common bucket will not get smaller if instead of working hard you do the bare minimum to avoid punishment and save the energy for your family or use it in a black market.