A good metaphor is something even the police should keep an eye on.
Source: Aphorisms, Notebook E, aph. 91 (written 1765 --99; tr. by R. J. Hollingdale, 1990).
-- G C Lichtenberg, (Jul 1 1742-1799), German physicist, writer; He is best known for his satirical wit ridiculing metaphysical and romantic excesses.