Communism's maxim of 'from each according to his capacity to each according to his needs' has two key parts. The first is decision making, and the second is reward.
The fatal flaw in my mind of the noble goal of prioritising the needs of everyone, is the central decision making. The reality as humans is our capacity to both think and feel is limited by biological constraints. The meat and bones that make up our abilities. If you put distance between decision makers and where those decisions are felt, things fall apart.
The second flaw is in the reward. Incentives. How do you get people to 'fill their capacity' and go further than they need to, to merely meet their own needs? They may exert effort for those close to them, but again... Our capacity to care is as limited as our capacity to think. Communism's answer in all the experiments of the last century was force.
Capitalism answer is trickery. The answer to the question 'How much is enough?' is more. By investing excess in Capital, others benefit. The owner notionally is in control, but in reality our capacity to make decisions is limited. We have to trust others. We have to delegate. Both Communist Dictators and Capitalist Control Freaks have to find a circle of people to make decisions, and take actions. We have to have people act on our behalf, and once again, the bigger the distance between actions and intentions, the more room for error.
Instead of owning big and bigger houses, more and more cars, etc., the trickery of Capitalism is to permit 'ownership' of a number. This shifts Conspicuous Hoarding towards productive assets. The stuff that makes that number grow may be factories making food, or houses, or cars... but the owner becomes incentivised to carry on working. Why does a Billionaire carry on working when they are spending as much as is humanly possible already? They just grow the number. More.
Both of these systems were dealing with a world of scarcity where the majority of us were in poverty. In material terms the contribution of global institutions, trade, democracy and increased cooperation have been hammering our collective poverty. Mixed economies which have tried to learn the lessons from failed systems of the past. An 'Establishment' that tweaks as it goes.
The next beautiful question is what happens once we have enough. What lies beyond enough?