Knowledge kills action, for action requires a state of being in which we are covered with the veil of illusion. - Friedrich Nietzsche

Knowledge kills action; action requires the veils of illusion.

"I can tell by my own reaction to it that this book is harmful." But let him only wait and perhaps one day he will admit to himself that this same book has done him a great service by bringing out the hidden sickness of his heart and making it visible. — Altered opinions do not alter a man’s character (or do so very little); but they do illuminate individual aspects of the constellation of his personality which with a different constellation of opinions had hitherto remained dark and unrecognizable.

Are designations congruent with things? Is language the adequate expression of all realities? It is only by means of forgetfulness that man can ever reach the point of fancying himself to possess a "truth" of the grade just indicated. If he will not be satisfied with truth in the form of tautology, that is to say, if he will not be content with empty husks, then he will always exchange truths for illusions.

The liar is a person who uses the valid designations, the words, in order to make something which is unreal appear to be real. He says, for example, "I am rich," when the proper designation for his condition would be "poor." He misuses fixed conventions by means of arbitrary substitutions or even reversals of names. If he does this in a selfish and moreover harmful manner, society will cease to trust him and will thereby exclude him. What men avoid by excluding the liar is not so much being defrauded as it is being harmed by means of fraud. Thus, even at this stage, what they hate is basically not deception itself, but rather the unpleasant, hated consequences of certain sorts of deception. It is in a similarly restricted sense that man now wants nothing but truth: he desires the pleasant, life-preserving consequences of truth. He is indifferent toward pure knowledge which has no consequences; toward those truths which are possibly harmful and destructive he is even hostilely inclined.