“Never attempt to teach a pig to sing; it wastes your time and annoys the pig.”
Source: Time Enough for Love
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Robert A. Heinlein 557
American science fiction author 1907–1988Related quotes

“Teach him how you will, a pig will never play the flute.”
Thom Merrilin
(15 January 1990)

“Never argue with a pedant over nomenclature. It wastes your time and annoys the pedant.”
Vorkosigan Saga, Memory (1996)
“A pig is a pig," said the stranger, "and a pig-boy is a pig-boy.”
Source: The Chronicles of Prydain (1964–1968), Book II: The Black Cauldron (1965), Chapter 1 (Ellidyr)
“A pig among people is a pig, he tells himself, but a pig among pigs is people.”
Section 38 (p. 118)
Venus Plus X (1960)

“I learned long ago never to wrestle with a pig. … You get dirty and besides the pig likes it.”
Initially attributed to Cyrus S. Ching in Time, Vol. 56 (1950), p. 21.
Misattributed
Variant: Never wrestle with pigs. You both get dirty and the pig likes it.

"Let's Play Minecraft - Episode 91 - Darwin Awards" https://www.youtube.com/watch?v=N3moj3zGYzk. youtube.com. February 21, 2014. Retrieved January 3, 2016.

AronRa vs Ray Comfort (September 17th, 2012), Radio Paul's Radio Rants

“You can put lipstick on a pig. It's still a pig.”