In psychology, adaptation-level phenomenon is the human tendency to adapt to stimuli while expecting future stimuli to be the same. The term was coined by author David G. Meyers.
Adaptation-level phenomenon is a term used in the study of happiness as discussed in David G. Meyers' book, "The Pursuit of Happiness." It refers to the theory that emotions and sensations are relative and quick to change. Humans tend to adapt to their surroundings and no longer respond to the novelty of certain stimuli after a period of time has passed. The phenomenon can manifest itself in a need for more and more stimuli to create the same effect; for example, someone addicted to gambling or high-speed racing needs more of a thrill each time to experience the same level of happiness.
After achieving success, such as a new job, a new romantic relationship or a new home, humans tend to experience euphoric feelings, only for those feelings to dissipate and become the new normal. This normal, or "neutral," feeling is relative. What excites one person seems dull to another. All experiences of success or failure hinge on the current neutrality. If a new development, occurrence or achievement seems better than the current state of affairs, a person feels happy, but only for a little while. If, however, the new development seems like a step backward, the person will feel sad and frustrated.