"The madman’s explanation of a thing is always complete, and often in a purely rational sense satisfactory. Or, to speak more strictly, the insane explanation, if not conclusive, is at least unanswerable; this may be observed specially in the two or three commonest kinds of madness. If a man says (for instance) that men have a conspiracy against him, you cannot dispute it except by saying that all the men deny that they are conspirators; which is exactly what conspirators would do. His explanation covers the facts as much as yours. Or if a man says that he is the rightful King of England, it is no complete answer to say that the existing authorities call him mad; for if he were King of England that might be the wisest thing for the existing authorities to do. Or if a man says that he is Jesus Christ, it is no answer to tell him that the world denies his divinity; for the world denied Christ’s.
"Nevertheless he is wrong. But if we attempt to trace his error in exact terms, we shall not find it quite so easy as we had supposed. Perhaps the nearest we can get to expressing it is to say this: that his mind moves in a perfect but narrow circle. A small circle is quite as infinite as a large circle; but, though it is quite as infinite, it is not so large. In the same way the insane explanation is quite as complete as the sane one, but it is not so large. A bullet is quite as round as the world, but it is not the world. There is such a thing as a narrow universality; there is such a thing as a small and cramped eternity; you may see it in many modern religions. Now, speaking quite externally and empirically, we may say that the strongest and most unmistakable MARK of madness is this combination between a logical completeness and a spiritual contraction. The lunatic’s theory explains a large number of things, but it does not explain them in a large way. I mean that if you or I were dealing with a mind that was growing morbid, we should be chiefly concerned not so much to give it arguments as to give it air, to convince it that there was something cleaner and cooler outside the suffocation of a single argument. . . .
"As an explanation of the world, materialism has a sort of insane simplicity. It has just the quality of the madman’s argument; we have at once the sense of it covering everything and the sense of it leaving everything out. Contemplate some able and sincere materialist, . . . and you will have exactly this unique sensation. He understands everything, and everything does not seem worth understanding. His cosmos may be complete in every rivet and cog-wheel, but still his cosmos is smaller than our world. Somehow his scheme, like the lucid scheme of the madman, seems unconscious of the alien energies and the large indifference of the earth; it is not thinking of the real things of the earth, of fighting peoples or proud mothers, or first love or fear upon the sea. The earth is so very large, and the cosmos is so very small. The cosmos is about the smallest hole that a man can hide his head in."
G. K. Chesterton, "Orthodoxy"