“It is one thing to show a man that he is in error, and another to put him in possession of the truth.”

Letter to Harrison Blake (20 May 1860); published in Familiar Letters (1865)
Context: Men and boys are learning all kinds of trades but how to make men of themselves. They learn to make houses; but they are not so well housed, they are not so contented in their houses, as the woodchucks in their holes. What is the use of a house if you haven't got a tolerable planet to put it on? — If you cannot tolerate the planet that it is on? Grade the ground first. If a man believes and expects great things of himself, it makes no odds where you put him, or what you show him … he will be surrounded by grandeur. He is in the condition of a healthy and hungry man, who says to himself, — How sweet this crust is!

Die Wahrheit widerspricht unserer Natur, der Irrthum nicht, und zwar aus einem sehr einfachen Grunde: die Wahrheit fordert, daß wir uns für beschränkt erkennen follen, der Irrthum schmeichelt uns. wir seien auf ein- oder die andere Weise unbegränzt.
Maxim 310, trans. Stopp
Maxims and Reflections (1833)

C'est une maladie naturelle à l'homme de croire qu'il possède la vérité directement…
Section I
Variant translation: It is man's natural sickness to believe that he possesses the Truth.
On the Spirit of Geometry

Vol. 2, Essais et Notes
The Lie of the Truth (1938)

"Religion: A Dialogue."
Variant translation: To free a man from error does not mean to take something from him, but to give him something.
Essays
Source: Essays and Aphorisms
Context: To free a man from error is to give, not to take away. Knowledge that a thing is false is a truth. Error always does harm; sooner or later it will bring mischief to the man who harbors it. Then give up deceiving people; confess ignorance of what you don't know, and leave everyone to form his own articles of faith for himself. Perhaps they won't turn out so bad, especially as they'll rub one another's corners down, and mutually rectify mistakes. The existence of many views will at any rate lay a foundation of tolerance. Those who possess knowledge and capacity may betake themselves to the study of philosophy, or even in their own persons carry the history of philosophy a step further.

Jacula Prudentum (1651)

Source: Aphorisms and Reflections (1901), p. 171-172

1880s, Garfield's Words (1882)

Source: Black Skin, White Masks