Excerpt from Plato's Apology
"And now, Athenians, I am not going to argue for my own sake, as you may think, but for yours, that you may not sin against the God, or lightly reject his boon by condemning me. For if you kill me you will not easily find another like me, who, if I may use such a ludicrous figure of speech, am a sort of gadfly, given to the state by the God; and the state is like a great and noble steed who is tardy in his motions owing to his very size, and requires to be stirred into life. I am that gadfly which God has given the state and all day long and in all places am always fastening upon you, arousing and persuading and reproaching you. And as you will not easily find another like me, I would advise you to spare me. I dare say that you may feel irritated at being suddenly awakened when you are caught napping; and you may think that if you were to strike me dead, as Anytus advises, which you easily might, then you would sleep on for the remainder of your lives, unless God in his care of you gives you another gadfly..."
Socrates (469–399 B.C.E.)
From Ludwig Wittgenstein's Tractatus Logico-Philosophicus
"What can be said, can be said with clarity: What can't be said, must remain unsaid ... The language defines the limit, beyond that limit is nonsense."
Tao Te King by Lao Tse, chapter one
(translated by Gia Fu Feng)
"The Tao that can be told is not the eternal Tao.
The name that can be named is not the eternal name.
The nameless is the beginning of heaven and Earth.
The named is the mother of the ten thousand things.
Ever desireless, one can see the mystery.
Ever desiring, one sees the manifestations.
These two spring from the same source but differ in name; this appears as darkness.
Darkness within darkness.
The gate to all mystery."