“We often cause ourselves suffering by wanting only to live in a world of valleys, a world without struggle and difficulty, a world that is flat, plain, consistent.”

Source: Lolita

Wir leben immer in einer Welt, die wir uns selbst bilden.
Übers Erkennen und Empfinden in der menschlichen Seele (1774); cited from Bernhard Suphan (ed.) Herders sämmtliche Werke (Berlin: Weidmann, 1877-1913) vol. 8, p. 252. Translation from Roy Pascal The German Sturm und Drang (Manchester: Manchester University Press, 1959) p. 136

“Waifs and Strays”, p. 25
The Ivory and the Horn (1996)

Preface
The Great Rehearsal (1948)

http://books.google.com/books?id=vQEzAAAAMAAJ&q=%22We+should+often+be+ashamed+of+our+very+best+actions+if+the+world+only+saw+the+motives+which+caused+them%22&pg=PA47#v=onepage
Nous aurions souvent honte de nos plus belles actions, si le monde voyoit tous les motifs qui les produisent.
http://books.google.com/books?id=X8akMrBxYegC&q=%22Nous%22+%22aurions+souvent+honte+de+nos+plus+belles+Actions+si+le+monde+voyoit+tous+les+motifs+qui%22+%22les+produisent%22&pg=PA232#v=onepage
Maxim 409.
Reflections; or Sentences and Moral Maxims (1665–1678)

All Gall Is Divided (1952)

On Truth and Lie in an Extra-Moral Sense (1873)
Context: Only by forgetting this primitive world of metaphor can one live with any repose, security, and consistency: only by means of the petrification and coagulation of a mass of images which originally streamed from the primal faculty of human imagination like a fiery liquid, only in the invincible faith that this sun, this window, this table is a truth in itself, in short, only by forgetting that he himself is an artistically creating subject, does man live with any repose, security, and consistency. If but for an instant he could escape from the prison walls of this faith, his "self consciousness" would be immediately destroyed. It is even a difficult thing for him to admit to himself that the insect or the bird perceives an entirely different world from the one that man does, and that the question of which of these perceptions of the world is the more correct one is quite meaningless, for this would have to have been decided previously in accordance with the criterion of the correct perception, which means, in accordance with a criterion which is not available.

Source: The Magician's Elephant

Variant: He who would live must fight. He who doesn't wish to fight in this world, where permanent struggle is the law of life, has not the right to exist.
Source: Mein Kampf