“Because we write fiction we mine our souls. Of course you put yourself into your fiction, your fiction is you.”

On Writing Poetry (1995)
Context: It's a feature of our age that if you write a work of fiction, everyone assumes that the people and events in it are disguised biography — but if you write your biography, it's equally assumed you're lying your head off. This last may be true, at any rate of poets: Plato said that poets should be excluded from the ideal republic because they are such liars. I am a poet, and I affirm that this is true. About no subject are poets tempted to lie so much as about their own lives; I know one of them who has floated at least five versions of his autobiography, none of them true. I of course — being also a novelist — am a much more truthful person than that. But since poets lie, how can you believe me?

Quoted in Mickey Pearlman, Listen to Their Voices (1993), ch. 12

Sec. 624, as translated by Tobias Dantzig in Number, the Language of Science. Fourth edition, New York: Doubleday 1954, p 141. See discussion of this entry for details.
The Will to Power (1888)

Source: Opus Posthumous: Poems, Plays, Prose

"How To Build A Universe That Doesn't Fall Apart Two Days Later" (1978)

Source: Children of the Mind

Divided by Infinity (p. 172)
The Perseids and Other Stories (2000)