The Master said, "Yu, shall I teach you what knowledge is? When you know a thing, to hold that you know it; and when you do not know a thing, to allow that you do not know it;—this is knowledge."
子曰、由、誨女知之乎、知之爲知之、不知爲不知、是知也。
Analects 2.17
The same idea in other traditions
Keep thy tongue from evil, And thy lips from speaking guile.
Truth is higher than everything; but higher still is truthful living.
O ye who believe! Fear Allah, and (always) say a word directed to the Right:
Lying lips are abomination to the Lord: but they that deal truly are his delight.
A man is not learned because he talks much; he who is patient, free from hatred and fear, he is called learned.
By simplicity he will become upright in actions, thoughts, and speech, and he will become veracious; thereby he will truly practise the Law.
The true prevails, not the untrue; by the true the path is laid out, the way of the gods (devayânah), on which the old sages, satisfied in their desires, proceed to where there is that highest place of the True One.
Little is known by any one but the spiritual man, / Who has in his heart a touchstone of vital truth. / The others, hovering between two opinions, / Fly towards their nest on a single wing. / Knowledge has two wings, opinion only one wing; / Opinion is weak and lopsided in its flight. …