Hedonic treadmill

Brickman and Campbell coined the term "Hedonic Treadmill" in their essay "Hedonic Relativism and Planning the Good Society" (1971), which appeared in M.H. Apley, ed., Adaptation Level Theory: A Symposium, New York: Academic Press, 1971, pp 287-302. The theory has consequences for understanding happiness as both an individual and a societal goal.

The concept was modified by Michael Eysenck, a British psychology researcher during the late nineties, to refer to the hedonic treadmill theory which compares the pursuit of happiness to a person on a treadmill, who has to keep working just to stay in the same place.

The Theory
Humans rapidly and inevitably adapt to good things by taking them for granted. The more possessions and accomplishments we have, the more we need to boost our level of happiness. It supposes that the brain of a species that has dominated others would evolve to strive for continual betterment.

Details

 * Despite the fact that external forces are constantly changing our life goals, happiness for most people is a relatively constant state. Regardless of how good things get, we'll always be about the same level of happiness.
 * It is believed that the baseline of an individual's happiness is at least partially genetic. For example, identical twins are usually equally bubbly or grumpy.
 * There are things that we can do to raise or lower our baseline happiness. Marriage does, pets do, but children don't seem to (despite what we think). Money does not add much to happiness. Lottery winners are the perfect example: within a year, they usually return to their former happiness level. Those handicapped in motor vehicle accidents are another example.  They too return to former happiness levels, despite their loss of function.