Basic economic theory teaches us that our needs are insatiable but our resources are limited in satisfying them. It is basic human nature to always want more - I would be hard-pressed to know anyone who would turn down a pay raise at work, all other things being equal. While our needs can be satisfied in the short-term, long-term underlying greed can never be satisfied.
There is enough for each man's need, but not each man's greed. However, each man's greed has actually offset the resources available for satisfying every man's need. For instance, we have countries with obesity problems, who willfully participate in competitive eating, and on the contrast we have countries whose high infant mortality rates are attributed to lack of food.