Shane Parrish writes in Clear Thinking:

Running on the hedonic treadmill only turns us into what I call “happy-when” people—those who think they’ll be happy when something happens. For example, we’ll be happy when we get the credit we deserve, or happy when we make a bit more money, or happy when we find that special someone. Happiness, however, isn’t conditional.

See also What You Can Achieve in 15-Minute Bursts of Creativity.