Man feels meaningless, empty, hollow within, and wants to fill it, stuff it. The effort to fill it somehow is greed. That effort is bound to fail for the simple reason because whatsoever you accumulate remains on the outside; it cannot reach within you. And the problem is within... and the solution you are seeking is without.
For example, you are feeling meaningless inside you and you are trying to fill it by money. It is a stupid effort, unconscious effort, not seeing a simple point: that money can be gathered, accumulated, but it will pile up around you. You can have mountains of money around you...there have been people with mountains of money.