"satisfaction treadmill. Suppose that in addition to adapting to particular objects or experiences, you also adapt to particular levels of satisfaction. In other words, suppose that with great ingenuity and effort in making decisions, you manage to keep your "hedonic temperature" at +20 degrees, so that you feel pretty good about life almost all of the time. Is +20 degrees good enough? Well, it might be good enough at the beginning, but if you adapt to this particular level of happiness, then +20 won't feel so good after a while."