The Art of Doing Science and Engineering: Learning to Learn (1991), p. 5
“You do not know, and will never know, who the Remnant are, nor what they are doing or will do.”
Source: Isaiah's Job (1936), IV
Context: In any given society the Remnant are always so largely an unknown quantity. You do not know, and will never know, more than two things about them. You can be sure of those — dead sure, as our phrase is — but you will never be able to make even a respectable guess at anything else. You do not know, and will never know, who the Remnant are, nor what they are doing or will do. Two things you do know, and no more: First, that they exist; second, that they will find you. Except for these two certainties, working for the Remnant means working in impenetrable darkness; and this, I should say, is just the condition calculated most effectively to pique the interest of any prophet who is properly gifted with the imagination, insight and intellectual curiosity necessary to a successful pursuit of his trade.
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Albert Jay Nock 68
American journalist 1870–1945Related quotes

“If you ask me to play myself, I will not know what to do. I do not know who or what I am.”
As quoted in Halliwell's Filmgoer's Companion (1988) by Leslie Halliwell, p. 622

al-Ghazali https://awakenthegreatnesswithin.com/35-inspirational-imam-al-ghazali-quotes-on-success/
Variant: Ask yourself three questions and you will know who you are. Ask 'What do you believe in? What do you hope for? But most important - ask what do you love?
Source: The Bronze Horseman (2001)

Variant translations
If you know others and know yourself, you will not be imperiled in a hundred battles; if you do not know others but know yourself, you win one and lose one; if you do not know others and do not know yourself, you will be imperiled in every single battle.
Know your enemy and know yourself, find naught in fear for 100 battles. Know yourself but not your enemy, find level of loss and victory. Know not thy enemy nor yourself, wallow in defeat every time.
Literal translation: Know [the] other, know [the] self, hundred battles without danger; not knowing [the] other but know [the] self, one win one loss; not knowing [the] other, not knowing [the] self, every battle must [be] lost.
Source: The Art of War, Chapter III · Strategic Attack

“You never know just what you can do until you try.”
Source: Revenge of the Witch

Source: Madness and Civilization: A History of Insanity in the Age of Reason

“You never know what's in a person's heart until they're tested, do you?”
Source: Fried Green Tomatoes at the Whistle Stop Cafe