As a matter of fact, have you never noticed that most conversations are simply monologues delivered in the presence of a witness? – Margaret Millar, The Weak-Eyed Bat, 1942

Oh, the things that go through my mind that I never say. Oh, the things I say that never go through my mind. – Robert Brault, rbrault.blogspot.com

And there is monologue disguised as dialogue, in which two or more men, meeting in space, speak each with himself in strangely tortuous and circuitous ways and yet imagine they have escaped the torment of being thrown back on their own resources. – Martin Buber (1878—1965), translated from German

Basically you are like two parallel lines which never meet. Dialogue seems to be impossible. All is monologue — you are talking to yourself and the other is talking to himself. Two monologues together look like a dialogue only in appearance. – Osho, The Revolution: Talks on Kabir, 1979