strictly in theory communism sounds like the best form of government. but it's a soul destroyer. if you ( a person) aren't allowed to own anything of real value, ( in a material sense) and are never rewarded for your extra efforts, and you will be called on for those efforts because all people can't work at the same level, you'll begin to see the futility of your.work. gradually people come to the place of trying to get over on the state. as production for thankless effort falls, need increases because this attitude and these actions spread system wide. at that point it becomes a closed ever tightening circle.as an example; your cllective farm has a quota of.grain set by an expert in statistics, not a farmer. but the farm can't supply this food because the Red October tractor factory has lazy workers.and why shouldn't they be lazy the state parts and supply office ( who get the same pay for just doing paperwork) don't bother get the parts forwarded to. the tractor plant so no parts no tractor no food. and on and on. most changes were long term, but the short.term causes came to the fore when collectivly, people came to realize that enough people in enough areas were dissatisfied that a real chance for change existed. they might have the opportunlties and rewards of freedom. unfortunately for some people the shock of the responsibilities of freedom was very difficult. as time goes on the material rewards start to be more widespread so it gets easier.