progressive enhancement / graceful degradation

This quotes by Mitch Hedberg  strikes me as a good metaphor for graceful degradation / progressive enhancement.

I like an escalator because an escalator can never break, it can only become stairs. There would never be an escalator temporarily out of order sign, only an escalator temporarily stairs. Sorry for the convenience.

Mitch Hedberg (American comedian, 1968 – 2005)