Question: why people in this world never be satisfied? 

Answer: I think we are just wired that way - if humans were the kind of species to lie back and smell the roses, we probably would still life in caves and hunt with stone spears. \nIf we do well and get something, we are happy only for a while. So if we want that happy feeling again, we obviously have to go out and try to get something else again to re-capture that feeling. Also, as we are successful and acquire something, we usually get admired (and envied) by the people around us, a rather pleasant feeling. This admiration by others probably is expressed in all kind of pro-creative ways, therefore making it likely that this trait will get passed on. \nSo it would seem that we have the whole weight of evolution weighing in against us when it comes to contendedness.
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