Why kids demand extra for everything? how to make them understand and satisfy?

Kids have a less developed maturity and sense of understanding. They dont know what is sufficient for them and what is not. They will always seem to ask and demand for more, though being furnished with all his necessities. It becomes important for us as parents how to teach kids the importance of efficiency.
It becomes important for us as parents how to teach kids the the importance of efficiency kids always tend to ask for more cause they are always unsatisfied with what they get. They need to be taught the importance being satisfied with what they get otherwise when they grow up they will face a lot of problem. This unsatisfaction leads to a lot of greed in future , way to teach the kids to be satisfied with what they get is by teaching them how much they need things in life and to understand limit  which should be never crossed.
If necessary they should be scolded and made to understand that asking for extra is not good at all and that they should be satisfied with what they have.
They should be read stories with morals teach the importance and the bad effects of greediness and how it is good to be satisfied with whatever we have.
If we can teach the kids the bad effects of being read only then they will learn to be satisfied with what they have and hence the problem of kids asking for extra even after being satisfied is solved