The desires and expectations of human beings tend to rise when their circumstances change.
The millionaire wants to make 2 million next year. A person who loses 10 pounds, wants to lose another 5.
This trend is known as the hedonistic treadmill and marketers and salespeople thrive on this tendency for people to always want more and more. Needless to say, this approach of never being satisfied, of not having or being enough, have been proven not to result in a lasting shift in happiness.
In this way, we can literally spend our entire lives in a hamster wheel, an endless rat race, setting goal after goal, not realizing that the carrot: the promise of lasting love and happiness, will always be just out of our reach.
REFERENCE
Brickman, Philip, et al. “Lottery Winners and Accident Victims: Is Happiness Relative?” Journal of Personality and Social Psychology, vol. 36, no. 8, 1978, pp. 917–927., doi:10.1037//0022-3514.36.8.917.