Hedonic adaptation
Also said as Hedonic treadmill, Reward fatigue, Getting used to it
Good things stop feeling as good as you get used to them. A reward is felt against what you have come to expect, not on its own.
It is why a game's numbers have to keep climbing, and why the loot that thrilled you in hour one is vendor trash by hour twenty. Brickman and Campbell proposed the treadmill in 1971. Later long-term studies, such as work by Lucas and by Diener, show that adaptation is often incomplete and differs from person to person.
Say it
“Do not raise the reward each time. Change its kind: after five gold drops, the next prize should be a new ability. Variety wears out more slowly than size.”
Where you’ve seen it
Diablo games escalate damage numbers from tens into the billions across their lifespans, largely to keep the same feeling alive.
Not to be confused with overjustification effect
Adaptation is about how strong a reward feels over time. Overjustification is about what happens to your interest in the activity.