“Man can act only because he can ignore.”

Law.
Table Talk (1689)

Preface, Second edition (21 June 1849)
The Nemesis of Faith (1849)

Variant translation: If someone is able to show me that what I think or do is not right, I will happily change, for I seek the truth, by which no one ever was truly harmed. Harmed is the person who continues in his self-deception and ignorance.
VI, 21
Source: Meditations (c. 121–180 AD), Book VI

Source: My Several Worlds (1954), p. 52 - 53
Context: Every event has had its cause, and nothing, not the least wind that blows, is accident or causeless. To understand what happens now one must find the cause, which may be very long ago in its beginning, but is surely there, and therefore a knowledge of history as detailed as possible is essential if we are to comprehend the present and be prepared for the future. Fate, Mr. Kung taught me, is not the blind superstition or helplessness that waits stupidly for what may happen. Fate is unalterable only in the sense that given a cause, a certain result must follow, but no cause is inevitable in itself, and man can shape his world if he does not resign himself to ignorance.

Source: Eleven Minutes

Source: Man's Search for Meaning

19 December 1749
Letters to His Son on the Art of Becoming a Man of the World and a Gentleman (1774)
Context: We must not suppose that, because a man is a rational animal, he will, therefore, always act rationally; or, because he has such or such a predominant passion, that he will act invariably and consequentially in pursuit of it. No, we are complicated machines; and though we have one main spring that gives motion to the whole, we have an infinity of little wheels, which, in their turns, retard, precipitate, and sometime stop that motion.

Poppin (1969)
Context: We can only take it so far, because man can only take it so far, lower self can only take it so far, and you have to realize that the public is only at a certain place. We won't see the day when the public accepts what we wanna project, even though they are accepting a lot now. By the time they're accepting it, maybe they'll be too old.... If it's total freedom, I guess the ultimate thing you can go into is total silence between the audience and performer, with the performer projecting something he doesn't even have to play. A total silence trip is the ultimate.... We do antagonize them psychologically. People look at us and react. They either go "Wow! Hey-hey-hey, baby!" and we say that's great. They're reacting and that's wonderful. It's better than them sitting there doing nothing. I say make them react — do whatever's in your power to move the audience, and if that's where it is, and there where it is with America, sex and violence, then I say project it.

Collected Aphorisms