From the wikipedia page for "Hedonic Treadmill," emphasis mine.
Headey (2008) concluded that an internal locus of control along with "positive" personality traits (notably low neuroticism) are the largest significant factors affecting one's subjective well-being (SWB). The author also found that adopting "non-zero sum" goals, that is those which enrich one's relationships with others and with society as a whole (family-oriented and altruistic goals), increase the level of SWB. Conversely, attaching importance to zero-sum life goals: career success, wealth, and social status, will have a small but nevertheless statistically significant negative impact on people's overall subjective well-being (even though the size of a household's disposable income does have a small, positive impact on SWB). Duration of one's education seems to have no direct bearing on life satisfaction. And contradicting set point theory, there is apparently no return to homeostasis after sustaining a disability or developing a chronic illness. These disabling events are permanent, and thus according to cognitive model of depression, may contribute to depressive thoughts and increase neuroticism (another factor found by Headey to diminish SWB). In fact disability appears to be the single most important factor affecting human subjective well being. The impact of disability on SWB is almost twice as large as that of the second strongest factor affecting life satisfaction—the personality trait of neuroticism.