Plato

Raphael's Plato from School of Athens, Vatican Museum

Plato— detail from School of Athens(1508)
by Raphael Sanzio (1483-1520)
Stanza della Segnatura, Vatican Museum

On Philosophical Writings
& Spiritual Illumination
I know indeed that others have written on the same subjects; but who they are, is more than they know themselves. Thus much at least, I can say about all writers, past or future, who say they know the things to which I devote myself, whether by hearing the teaching of me or of others, or by their own discoveries that according to my view it is not possible for them to have any real skill in the matter. There neither is nor ever will be a treatise of mine on the subject. For it does not admit of exposition like other branches of knowledge; but after much converse about the matter itself and a life lived together, suddenly a light, as it were, is kindled in one soul by a flame that leaps to it from another, and thereafter sustains itself.

— Plato (428-348 B.C.), Seventh Letter(360 B.C.)
Translated by J. Harward (click to read complete 7th Letter).