hedonic treadmill
a metaphor for a hypothesis proposing that people’s happiness tends to return to a preexisting baseline level after positive or negative life events have occurred. According to this concept, positive and negative events may produce short-term shifts in mood, but these shifts tend to erode in a relatively brief period of time. This process of adaptation is thought to be responsible for the persistence of mood states over time, often in the face of considerable efforts to change them. Although there is good evidence for this hypothesis, research has demonstrated that people do not always return to baseline after the occurrence of mood-changing events. See also set point. [coined by Canadian-born U.S. psychologist Philip Brickman (1943–1982) and Donald Campbell in a 1971 essay]