"At the height of being in love the boundary between ego and
    object threatens to melt away. Against all the evidence of
    his senses, a man who is in love declares that 'I' and 'you'
    are one, and is prepared to behave as if it were a fact."

   "[E]ven the feeling of our own ego is subject to disturbances
    and the boundaries of the ego are not constant."

   "We are so made that we can derive intense enjoyment only
    from a contrast and very little from a state of things."

   "[I]t is impossible to overlook the extent to which 
    civilization is built upon a renunciation of instinct, how
    much it presupposes precisely the non-satisfaction of
    powerful instincts. This 'cultural frustration' dominates
    the large field of social relationships between human 
    beings."

    - Sigmund Freud (1856-1939), Civilization and Its Discontents