We have blind, one-eyed, cross-eyed, and squinting people, and visions long, short, clear, confused, weak, or indefatigable. All this is a faithful image of our understanding; but we know scarcely any false vision. There are not many men who always mistake a rooster for a horse, or a chamber pot for a house. How is it that we often meet with minds, otherwise judicious, that are absolutely wrong in some things of importance? How is it that the same Siamese man who can never be fooled when he is supposed to receive three rupees, firmly believes in the metamorphoses of Sammonocodom...

If these besotted beings are shown a little geometry, they learn it easily enough; but, strange to say, this does not set them right. They perceive the truths of geometry; but it does not teach them to weigh probabilities: they have taken their bent; they will reason falsely all their lives; and I am sorry for them.

-Voltaire, Philosophical Dictionary