Hedonic adaptation is the observed psychological tendency to revert back to prior levels of happiness soon after experiencing something pleasurable. The psychologists Brickman and Campbell began studying this phenomenon scientifically in the 1970s, calling it the Hedonic Treadmill. Hedonic adaptation accounts for our tendency to overestimate how happy pleasurable experiences will make us, and the fact that we tend to maintain a relatively stable level of happiness regardless of our material circumstances. It also explains our unfortunate human habit of taking what we have for granted.
Even though the Hedonic Treadmill was scientifically observed in recent history, it turns out that Kant possessed a remarkably similar insight into human psychology, simultaneously defining hedonic adaptation and changing the course of one man's life in an impromptu late night meeting in 1789.