was first used by William Cowper
in The Time-piece
(1785), the second book of his six-volume epic poem The Task
Variety's the very spice of life,
That gives it all its flavour.
It's an interesting observation, and one that rings true, at least in part. In a society dominated by fascination with extremity and boredom with subtlety, it's understandable why millions of people watch NASCAR and the WWF. When the brain becomes dulled to the newest shock, it seeks out new diversions to satiate the need for newness, as evidenced by the advent of dildo-cam in porn, television shows such as Big Brother and Survivor, and the increasing popularity of anal sex and autoerotic asphixiation.
However, human beings are also very comfortable with repetition and routine, and significant changes in daily activities, location, or surrounding objects and people often carry with them dramatic increases in stress and mental strain. The trick is to find variety within the routine; therein lies the spice of life.