[rsp1984]

When I see rich people being greedy, I find it hard to imagine how much worse they would be as human beings if they were poor.

They probably are poor, at least from their viewpoint, because humans like to compare themselves against their peers, not against the average person they have nothing to do with.

So rich people compare themselves against other rich people in their social circle and then decide they want to have a little more. It's not greed from their viewpoint, it's "not falling behind".