“Man's most valuable trait
is a judicious sense of what not to believe.”
The Complete Greek Tragedies: Euripides II: Helen. Hecuba. Andromache. The Trojan women. Ion. Rhesus. The suppliant women by David Grene, Richmond Alexander Lattimore (eds.), Modern Library, 1963, p. 73
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Euripidés 116
ancient Athenian playwright -480–-406 BCRelated quotes

“Time is the most valuable thing a man can spend.”
Diogenes Laërtius, Lives and Opinions of Eminent Philosophers, Book 5.

“Our most valuable and most instructive materials in the history of man are treasured up in India.”
Max Müller, India: What Can India Teach Us? (1883), p. 15 http://books.google.com/books?id=pIVDAAAAYAAJ&pg=PA15&dq=%22most+valuable+and+most+instructive+materials+in+the+history+of+man+are+treasured+up+in+India%22
Misattributed
Philosophy and Living (1939)
Context: Throughout man's career intelligence and charity have been man's distinctive and most valuable assets. One of our early pre-human ancestors is said to have been much like the Spectral Tarsier, a little mammal about the size of a mouse, with long wiry fingers and huge forward-looking eyes adapted for binocular vision. Not by weapons but by correlation of subtle eyes and subtle hands through subtle brain, this creature triumphed. And man himself conquered the world by the same means, by attention, by discrimination, by skilled manipulation, by versatility; in fact by intelligence and imagination in adapting himself to an ever-changing environment.

Theophrastus, 10.
The Lives and Opinions of Eminent Philosophers (c. 200 A.D.), Book 5: The Peripatetics

Cultural Anthropology and Psychiatry (1932), p. 515

“O! what a prodigal have I been of that most valuable of all possessions — Time!”
Last recorded words, as quoted in The Encyclopædia Britannica (1910)

Credo (1965)
Context: I believe that love is the main key to open the doors to the "growth" of man. Love and union with someone or something outside of oneself, union that allows one to put oneself into relationship with others, to feel one with others, without limiting the sense of integrity and independence. Love is a productive orientation for which it is essential that there be present at the same time: concern, responsibility, and respect for and knowledge of the object of the union.
I believe that the experience of love is the most human and humanizing act that it is given to man to enjoy and that it, like reason, makes no sense if conceived in a partial way.