A CRAB, forsaking the seashore, chose a neighboring green meadow
as its feeding ground.  A Fox came across him, and being very
hungry ate him up.  Just as he was on the point of being eaten,
the Crab said, "I well deserve my fate, for what business had I
on the land, when by my nature and habits I am only adapted for
the sea?' 

Contentment with our lot is an element of happiness.