Obtaining something we want follows a very stereotyped course, as noted in Oscar Wilde's famous aphorism: "There are only two tragedies in life: one is not getting what one wants, and the other is getting it." Or, consider the scene from the musical "Stop the World, I want to get off." in which the character at the climax of a song are entwined in a happy summation...the music stops...the characters keep holding their position, and keep holding....and keep holding...begin to wobble just a bit...wobble a bit more...and finally fall apart.
Why is the warm glow on attaining some we desire sustained? Why is happily-ever-after so rare? The issue, in terms of relationships, is addressed in Jane Brody recent review of writing and studies on keeping love alive in relationships. The happiness boost that occurs with marriage lasts only about two years, after which people revert to their former levels of happiness - or unhappiness, and infatuation and passion have even shorter life spans. The phenomenon is dubbed "hedonic adaptation" by psychologists - things that thrill us tend to be short-lived. (The reaction of many brain circuits to repeated stimulation is to decrease their reactivity or output, an example being the mesolimbic dopamine system, whose role in the brain reward system is controversial.)
Lyubomirsky's new book "The Myth of Happiness" deals with this situation and notes techniques, backed by recent research, that help relationships evolve into companionate love, composed more of deep affection, connection and liking (I just downloaded a test sample from Amazon to my iPad to check it out). Barbara L. Fredrickson, author of the forthcoming "Love 2.0" specifies that a flourishing relationship needs three times as many positive emotions as negative ones.
The advice on relationships all seems to boil down to "practice a bit more kindness and gratitude". I have to say, that when I've been able to budge my curmudgeonly nature enough to actually do this for brief periods of time, it has worked wonders!