It might sound silly, but I think it is the way we push evolution forward. Like, we had the desire to fly, travel faster, have a nice anonymous chat (EP)....
Hmm I definitely would not like to think that I evolve out of greed. However, there must be something pushing me forward... however it may be called... :)
We live in what Buddhists call a "Desire Realm", we want things. It's what makes us be born and die, and causes us to age.
I think it's a selfish kind of thing. Every human has the plague to contend with and it is both taught and instinctual.
I find happiness is too dependent on others. I have discovered it is senseless to be happy when you know a rapist is at work. Happiness depends on good company so I don't count on happiness anymore. I think self respect is the key. Understand you have full control over who you are and be the best you know how (which ironically leads into a constant loop of learning since there are always things to improve). In the end, you can be satisfied with your choices and understand you are only sad because you care about someone else.
It's a learned behavior,spare the rod,spoil the child,they will take it into adulthood.