Why?

why is it that all people want somthing that they know they shouldnt or can't have. its odd, for the things that you want are not things that you need, it never is. lots of people want cars but they dont NEED them. i mean why the hell is it so imparitive to have such things, im not just meaning material things im also meaning unsubstatial things like love or respect. no one needs it. but people want it.