Believe it or not, it’s interruption:

Six studies demonstrate that interrupting a consumption experience can make pleasant experiences more enjoyable and unpleasant experiences more irritating, even though consumers avoid breaks in pleasant experiences and choose breaks in unpleasant experiences. Across a variety of hedonic experiences (e.g., listening to noises or songs, sitting in a massage chair), the authors observe that breaks disrupt hedonic adaptation and, as a result, intensify the subsequent experience.

Source: “Interrupted Consumption: Disrupting Adaptation to Hedonic Experiences” from the Journal of Marketing Research