According to the hedonic treadmill theory of subjective well-being each human has a hedonic set point. Positive or negative life events cause relatively short-term deviations to one’s happiness before it returns to the baseline happiness level determined by the set point. The set point appears to be stable over the course of one’s life. One’s happiness, measured over time, looks something like this:
Question: What, if anything, has been demonstrated by research to cause long-term, significant upward shifts of the baseline happiness? And, if so, which of those interventions are accessible to an average person (in wealthy countries)?