“Do not counsel what is most pleasant, but what is best.”
Demetrius of Phalerum, "Apophthegms of the Seven Sages," in Early Greek Philosophy, vol. 2 (Loeb Classical Library, volume 525), p. 141
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Athenian legislator -638–-558 BCRelated quotes

“The best work is not what is most difficult for you; it is what you do best.”
Act 6, sc. 2
Dirty Hands (1948)

“It was not pleasant to admit what one is willing to do to go on living.”
Source: The Ophiuchi Hotline (1977), Chapter 14 (p. 141)

Heroism
1840s, Essays: First Series (1841)

“The most basic question is not what is best, but who shall decide what is best.”

Science Fiction on the Titanic, in Brian Aldiss and Harry Harrison (eds.) The Year's Best SF 9 (1976), ISBN 0-8600-7894-9, p. 201

“If you can do what you do best and be happy, you're further along in life than most people.”
http://www.popmonk.com/actors/leonardo-dicaprio/quotes-leonardo-dicaprio.htm

"Wherefore Wildlife Ecology?" [1947]; Published in The River of the Mother of God and Other Essays by Aldo Leopold, Susan L. Flader and J. Baird Callicott (eds.) 1991, p. 337.
1940s

“We teach best what we most need to learn.”
Illusions : The Adventures of a Reluctant Messiah (1977)
Variant: You teach best what you most need to learn.
Source: Illusions: The Adventures of a Reluctant Messiah