“The truth is, no study is possible on the battle-field; one does there simply what one can in order to apply what one knows. Therefore, in order to do even a little, one has already to know a great deal and to know it well.”

The Principles of War (1913)

Encountering Directors interview (1969)
Context: When a scene is being shot, it is very difficult to know what one wants it to say, and even if one does know, there is always a difference between what one has in mind and the result on film. I never think ahead of the shot I'm going to make the following day because if I did, I'd only produce a bad imitation of the original image in my mind. So what you see on the screen doesn't represent my exact meaning, but only my possibilities of expression, with all the limitations implied in that phrase. Perhaps the scene reveals my incapacity to do better; perhaps I felt subconsciously ironic toward it. But it is on film; the rest is up to you.

This Business of Living (1935-1950)

Dans l'amitié comme dans l'amour on est souvent plus heureux par les choses qu'on ignore que par celles que l'on sait.
Variant translation: In friendship as in love, we are often happier due to the things we are unaware of than the things we know.
Maxim 441.
Reflections; or Sentences and Moral Maxims (1665–1678)

Source: The Hunt for Red October

Ancient Medicine
Context: Certain s and physicians say that it is not possible for any one to know medicine who does not know what man is, and that who ever would cure men properly, must learn this in the first place. But this saying rather appertains to philosophy, as Empedocles and certain others have described what man in his origin is, and how he first was made and constructed. But I think whatever such has been said or written by sophist or physician concerning nature has less connexion with the art of medicine than with the art of painting. And I think that one cannot know anything certain respecting nature from any other quarter than from medicine... Wherefore it appears to me necessary to every physician to be skilled in nature, and strive to know... what man is in relation to the articles of food and drink, and to his other occupations, and what are the effects of each of them to every one.<!--pp. 174-175

Sie muss also zu weit gehen, um herauszufinden, wie weit sie gehen darf.
"Die Freiheit der Kunst", speech delivered at Wuppertal on September 24, 1966; cited from Cultura 21 magazine http://www.cultura21.de/magazin/denkanstosse/d20050930a.html, September 30, 2005. Translation: Walter Laqueur Germany Today: A Personal Report (London: Weidenfeld and Nicolson, 1985) p. 130.

Ask the Awakened: the Negative Way (1963)