hedonic adaptation

This makes a lot of sense:

The hedonic treadmill, also known as hedonic adaptation,
is the tendency of a person to remain at a relatively stable level of
happiness despite changes in fortune or the achievement of major goals.
As a person makes more money, expectations and desires rise in tandem,
which results in no permanent gain in happiness.

-Chris Hall's status on facebook earlier today

This also explains the usual tendency for scope creep in projects.
(Chris is a high school friend of mine and currently teaches languages at a Montreal CEGEP when he's not busy observing the world)