Many books serve merely to show how many ways there are of being wrong, and how far astray you yourself would go if you followed their guidance. You should read only when your own thoughts dry up.
As the biggest library if it is in disorder is not as useful as a small but well-arranged one, so you may accumulate a vast amount of knowledge but it will be of far less value than a much smaller amount if you have not thought it over for yourself.
Consider the Koran... this wretched book was sufficient to start a world-religion, to satisfy the metaphysical need of countless millions for twelve hundred years, to become the basis of their morality and of a remarkable contempt for death, and also to inspire them to bloody wars and the most extensive conquests. In this book we find the saddest and poorest form of theism. Much may be lost in translation, but I have not been able to discover in it one single idea of value.
Boredom is an evil that is not to be estimated lightly. It can come in the end to real despair. The public authority takes precautions against it everywhere, as against other universal calamities.
Man may have the most excellent judgment in all other matters, and yet go wrong in those which concern himself; because here the will comes in and deranges the intellect at once. Therefore let a man take counsel of a friend. A doctor can cure everyone but himself; if he falls ill, he sends for a colleague.
Scholars are those who have read in books, but thinkers, men of genius, world-enlighteners, and reformers of the human race are those who have read directly in the book of the world.
The fourfold root of the principle of sufficent reason is "Anything perceived has a cause. All conclusions have premises. All effects have causes. All actions have motives.
Every time a man is begotten and born, the clock of human life is wound up anew to repeat once more its same old tune that has already been played innumerable times, movement by movement and measure by measure, with insignificant variations.