“All the people in the Kuo-ch'ing monastery—
They say, "Han-shan is an idiot."
"Am I really an idiot:" I reflect.
But my reflections fail to solve the question:
for I myself do not know who the self is,
And how can others know who I am?”

Source: The Chronicles of Prydain (1964–1968), Book IV: Taran Wanderer (1967), Chapter 21
Context: “I saw myself,” Taran answered. “In the time I watched, I saw strength – and frailty. Pride and vanity, courage and fear. Of wisdom, a little. Of folly, much. Of intentions, many good ones; but many more left undone. In this, alas, I saw myself a man like any other.
“But this, too, I saw,” he went on. “Alike as men may seem, each is different as flakes of snow, no two the same. You told me you had no need to seek the Mirror, knowing you were Annlaw Clay-Shaper. Now I know who I am: myself and none other. I am Taran.”

Statement recorded in the diary of his companion Johanna Fantova, quoted at the end of the New York Times story "From Companion's Lost Diary, A Portrait of Einstein in Old Age" http://www.nytimes.com/2004/04/24/nyregion/from-companion-s-lost-diary-a-portrait-of-einstein-in-old-age.html?pagewanted=all&src=pm by Dennis Overbye (24 April 2004)
Attributed in posthumous publications

Interview to Cosmopolitan (2016)

1990s, Schafer interview (1995)

As quoted in Halliwell's Filmgoer's Companion (1988) by Leslie Halliwell, p. 622

Liv Tyler On Her Iconic Career, Living Through Fame And The Importance Of Female Friendship http://www.oystermag.com/2018/11/liv-tyler-on-her-iconic-career-living-through-fame-and-the-importance-of-female-friendship-for-oyster-115/ (November 28, 2018)

Biff
Source: Death of a Salesman (1949)

”I have no idea what kind of idiot you are,” Miss Jesczenka said. “That’s why I’m asking.”
Source: The Hidden Goddess (2011), Chapter 8, “Chaos and Disorder” (p. 133)