“Not to be absolutely certain is, I think, one of the essential things in rationality.”

7 Absolute Honesty, p. 8.
The Everything and the Nothing (1963)
Context: Absolute honesty is essential in one's search for God (Truth). The subtleties of the Path are finer than a hair. The least hypocrisy becomes a wave that washes one off the Path.
It is your false self that keeps you away from your true Self by every trick it knows. In the guise of honesty this self even deceives itself. For instance your self claims, I love Baba. The fact is, if you really loved Baba you would not be your false self making the self-asserting statement!

Free the Airwaves! (2002)

Patrick L. McGuire, Her Strong Enchantments Failing (p. 93; this work is an essay about Anderson's story The Queen of Air and Darkness).
Short fiction, The Book of Poul Anderson (1975)

Norah Vincent, Sex, Love and Politics: Andrea Dworkin, in New York Press, vol. 11, no. 5, Feb. 4–10, 1998, p. 40, col. 4 (main title and subtitle may have been in either order, per id., p. [1]).

Source: The Lover's Dictionary

When Pausch spoke of "when you’re screwing up and nobody’s saying anything to you anymore, that means they gaveup." he was quoting Jon Snoddy http://www.snoddy.net/
The Last Lecture (2007)
Context: Wait long enough and people will surprise and impress you. He said, when you are pissed off at somebody, and you're angry at them, you just haven't given them enough time. Just give them a little more time — and they'll almost always impress you. And that really stuck with me. I think he's absolutely right on that one.

Section 57
The True Believer (1951), Part Three: United Action and Self-Sacrifice
Context: We can be absolutely certain only about things we do not understand. A doctrine that is understood is shorn of its strength.