Basically, the problem with Communism is that it goes against nature. In nature, the animals that are the strongest and most skilled, or use the best strategies for hunting are the ones that survive.
Fuzzmosis has the very fundamentals. in communism, every body works, and everyone gets the same amount, if they work hard, they get paid one amount, and if they don't work hard, they STILL get paid the same amount.
ZERO motivation.
People will naturally slack off or at the very least do the bare minimum. This isn't just a matter of being lazy either, this is a basic case of reinforcing behavior. Even the most dedicated person in the world is not going to be able to put forth their best effort when they are constantly being shown that they get absolutely NOTHING for that best effort.
So how does any work get done at all? Well, that's when the government begins telling you that if you don't work the way they decide you should work, they'll kill you, or take your kids away from you, or basically throw you in chains for forced labor.
And what can the people do about it? They're in a communism, they don't even own their own money, because the government is the one who decides who gets how much. You can be sure as heck certain that the government is going to outlaw guns so that they can't have a revolution too.
Capitalism isn't always pretty, sometimes it's ruthless, and most of the time it doesn't feel fair at all, but that's just how life is. Those who put forth the most effort get the most out of it. Sometimes life throws lucky breaks, sometimes people get by on other peoples effort, but no matter what happens around you, there is still that chance to change your life for the better that is always present. Sometimes it takes a lot of risk, far more time and way too many failed attempts, but you are still ultimately the one in control of your own life.
Capitalism also has one other major advantage over communism, which is the creation of new wealth.
Almost every other system that addresses monetary issues is based on the principle that if you want to make money, there has to be someone else to make it from. if I want to make $10, someone else has to lose $10, and then for them to make back that $10 to break even, they in turn have to make $10 off of someone else, who will in turn do the same and on and so on.
Capitalism allows a person to consider the perceived value of an object.
for instance, in most places in America, you can find drinking fountains scattered wherever. for all intents and purposes, water is free. If someone told you to pay $50 for a bottle of water, you'd laugh at them. But what if you were in the middle of a desert, dying of a 3 day period with no water? Suddenly the price isn't quite so bad.
Now in that example, one person is taking advantage of the other. But what if both of them take advantage of each other at the same time? There's the phrase "one man's trash is another man's treasure." If you have something that is useless to you, but is the exact thing the other guy absolutely NEEDS, but he has something useless to him that YOU need, you both trade, and you both gave away something that was worth $0 and got something in return that was worth $50 -$1000. The $50 - $1000 didn't come from the other guy, it is new wealth.
so yeah, that's a pretty basic summation of why communism doesn't work in reality, and why capitalism does.