Adaptation-level phenomenon is the tendency to adapt to a given level of stimulation and thus to notice and react to changes from that level.
The basic point is that we use our past to calibrate our present experience and to form expectations for the future. Success and failure, satisfaction and dissatisfaction, are relative to our prior experience. If our achievements rise above those expectations, we experience success and satisfaction. If our achievements fall below the neutral point defined by prior experience, we feel dissatisfied and frustrated.
List of books: Adaptation-level,phenomenon