Indeed the reasoned criticism of a prevailing belief is a service to the proponents of that belief; if they are incapable of defending it, they are well advised to abandon it. This self-questioning and error-correcting aspect of the scientific method is its most striking property.
Concepts which have proved useful for ordering things easily assume so great an authority over us, that we forget their terrestrial origin and accept them as unalterable facts. They then become labeled as 'conceptual necessities,' etc. The road of scientific progress is frequently blocked for long periods by such errors.
The error of Socrates must be attributed to the false notion of unity from which he starts. Unity there should be, both of the family and of the state, but in some respects only. For there is a point at which a state may attain such a degree of unity as to be no longer a state, or at which, without actually ceasing to exist, it will become an inferior state, like harmony passing into unison, or rhythm which has been reduced to a single foot. The state, as I was saying, is a plurality which should be united and made into a community by education
So may the outward shows be least themselves: The world is still deceived with ornament. In law, what plea so tainted and corrupt, But, being seasoned with a gracious voice, Obscures the show of evil? In religion, What damned error, but some sober brow Will bless it and approve it with a text, Hiding the grossness with fair ornament? There is no vice so simple but assumes Some mark of virtue on his outward parts.
If at times I have thought myself unfortunate, it is because of a confusion, an error. I have mistaken myself for someone else... Who am I really? I am the author of The World as Will and Representation, I am the one who has given an answer to the mystery of Being that will occupy the thinkers of future centuries. That is what I am, and who can dispute it in the years of life that still remain for me?
It is too often believed that a person in his progress towards perfection passes from error to truth; that when he passes on from one thought to another, he must necessarily reject the first. But no error can lead to truth. The soul passing through its different stages goes from truth to truth, and each stage is true; it goes from lower truth to higher truth.
There is only one inborn erroneous notion ... that we exist in order to be happy ... So long as we persist in this inborn error ... the world seems to us full of contradictions. For at every step, in great things and small, we are bound to experience that the world and life are certainly not arranged for the purpose of maintaining a happy existence ... hence the countenances of almost all elderly persons wear the expression of ... disappointment.
To free a man from error is to give, not to take away. Knowledge that a thing is false is a truth. Error always does harm; sooner or later it will bring mischief to the man who harbors it.
Zarathustra was the first to consider the fight of good and evil the very wheel in the machinery of things: the transposition of morality into the metaphysical realm, as a force, cause, and end in itself, is his work. [...] Zarathustra created this most calamitous error, morality; consequently, he must also be the first to recognize it.