"Another thought occurs: perhaps happiness is in inverse relationship to intelligence. In our first and second childhoods, we are tolerably happy, but intellectually challenged; only in the middle of our lives are we clever enough to realise that life is utterly meaningless, directed towards death and that the unlikelihood of an afterlife means that we have no rational justification for turning that existential frown upside down?" Stuart Jefferies.
Like this it might be that we are faced with the existential questions around the time where it seems to be more or less you should be happy with the certain condition you are under or have achieved (so hard to get even).. such as a proper job, a stable marriage or a suitable partner, house etc are secured. Ofcourse it does not mean that you do not question your existence and the "meaning of life" when you are not secured.
Whichever the case, it just is that some of us, will not let ourselves alone and face the question of life, "what is it I am doing?", "what is my life my goal?" and the sort, even when the more major things in life has been satisfied. Or atleast the most premitive needs...
Of course there are some of us who are forever unhappy due to the pure fact that they compare their situations with others, who have abit more of something then us... whatever that may be. And then there are those who are forever searching for another step. That is, after you build a foundation, you need steady pillars and then right walls, the a good ceiling and paint, furniture...
It can be good if this is a positive stress, to further yourself in life, to have something to put your energy towards in your life.
It can be a bad thing, if you are insatiable and always unhappy with whatever that is given to you.
Then again, its one thing to want something and another to question the things you have right now or the situation you are in... such as examining the relationship you have right now, it is related in the sense that when you question, alot of the time you can be unsatisfied with your situation and want better things.