You know, there is a famous American proverb : "the grass is always greener on the other side", I would add: the neighbour's wife is better, friend's car is faster etc.. And also there is no limit for people desire. This is what human being is all about.
True. Humans will always yearn for better things, and this often leads to greed. In a macro scale, look at all these countries trying to outsmart and outdo each other. They try to amass as much wealth as possible, they event try to take each other's the resources. The results are ugly. It's taken a toll on the environment and is also threatening our lives.