I actually have a psychological theory. In it i wrote that i consider true satisfaction to be an imposibility.
We are defined by our goals and ends, these goals do not have to be material but they are inherently how we define our purpouse. Whenever we acheive something we almost imediatly turn our eyes to something else. If we were trully ever satisfied we would have no goals or ends, which i think makes us feel a lack of purpouse.
Why is it that we feel this way, i think it has something to do with the survival instincts we evolved with. Pain and displeasure is the natural state, because its the displeasure that makes us seak pleasure, if we were satisfied with no food or satisfied with no sex we would not seek it out. And i think the same goes for the more sophisticated goals we develop after the basic ones have been fulfiled. Not having ends makes us feel a lack of purpouse and having them means in itself that theres a lack of satisfaction.
I think this is why statistically sucessfull and rich people are just as unhappy as poor and midleclass people. No mater how much we acheive we always want more its in our nature. And when there is no more physical goals to acheive the conflict tends to become internal.
I think this is also part of the apeal of spirituality to some people. Living a good life with acordance to various doctorines is a task that seems atainable, but not untill ones life is over, so its and end that one be completly devoted to and yet never really reach. I find this kind of faith persaonaly top be more or less a usefull delusion.