Human selfishness.
In a perfect world with perfect people who only thought of others and never of themselves, communism would be ideal.
But in the real world people who work extra hard or take risks want to be rewarded, and resent those who slack off and do nothing but demand to be taken care of.
Communism will never work for one simple reason. The minute a decision has to be made Communism is done.
The phrase that best describes Communism is, “Now what?”
Communism is an unbridled lust for power with no clue how to actually govern. Like the dog who chases the car and finally catches it. “I caught the car, Now what?” Like Obama’s Presidency. “I became President, Now what?”
If an alien came to earth and saw Communism in action, they would probably say it was a virus.
As I see it, Communism is an ideological cover for a criminal enterprise which steals from the people to feed its own greed.
Adam Smith, The Wealth of Nations, vol.1, p.16
He was EXACTLY correct!
You are thinking of socialism. Communism fails because of too much centralization.