“To the untrue man, the whole universe is false- it is impalpable- it shrinks to nothing within his grasp. And he himself is in so far as he shows himself in a false light, becomes a shadow, or, indeed, ceases to exist.”

Source: Nightwood (1936), Ch. 6 : Where the Tree Falls

Niebla [Mist] (1914)
Context: Whenever a man talks he lies, and so far as he talks to himself — that is to say, so far as he thinks, knowing that he thinks — he lies to himself. The only truth in human life is that which is physiological. Speech — this thing that they call a social product — was made for lying.

Lecture given in 1946 (Existentialism from Dostoyevsky to Sartre, ed. Walter Kaufman, Meridian Publishing Company, 1989;) http://www.marxists.org/reference/archive/sartre/works/exist/sartre.htm (1946)
Context: Dostoevsky once wrote: “If God did not exist, everything would be permitted”; and that, for existentialism, is the starting point. Everything is indeed permitted if God does not exist, and man is in consequence forlorn, for he cannot find anything to depend upon either within or outside himself. He discovers forthwith, that he is without excuse.

Section IX, "Man Alone with Himself" / aphorism 513
Human, All Too Human (1878), Helen Zimmern translation

Source: Autobiography of a Yogi

25 May 1830
Table Talk (1821–1834)

[Paraphrasing Kant] p. 162.
Sex and Character (1903)

Tanto è miser l'uom quant' ei si riputa.
Ecloga Octava; reported in Hoyt's New Cyclopedia Of Practical Quotations (1922), "Mind".

La difficulté attire l'homme de caractère, car c'est en l'étreignant qu'il se réalise lui-même.
in Mémoires de guerre.
Writings