Such is the madman of experience; he is commonly a reasoner, frequently a successful reasoner. Doubtless he could be vanquished in mere reason, and the case against him put logically. But it can be put much more precisely in more general and even aesthetic terms. He is in the clean and well-lit prison of one idea: he is sharpened to one painful point. He is without healthy hesitation and healthy complexity. Now, as I explain in the introduction, I have determined in these early chapters to give not so much a diagram of a doctrine as some pictures of a point of view. And I have described at length my vision of the maniac for this reason: that just as I am affected by the maniac, so I am affected by most modern thinkers. That unmistakable mood or note that I hear from Hanwell, I hear also from half the chairs of science and seats of learning to-day; and most of the mad doctors are mad doctors in more senses than one. They all have exactly that combination we have noted: the combination of an expansive and exhaustive reason with a contracted common sense. They are universal only in the sense that they take one thin explanation and carry it very far. But a pattern can stretch for ever and still be a small pattern. They see a chess-board white on black, and if the universe is paved with it, it is still white on black. Like the lunatic, they cannot alter their standpoint; they cannot make a mental effort and suddenly see it black on white.

Take first the more obvious case of materialism. 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, as, for instance, Mr. McCabe, 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.

It must be understood that I am not now discussing the relation of these creeds to truth; but, for the present, solely their relation to health. Later in the argument I hope to attack the question of objective verity; here I speak only of a phenomenon of psychology. I do not for the present attempt to prove to Haeckel that materialism is untrue, any more than I attempted to prove to the man who thought he was Christ that he was labouring under an error. I merely remark here on the fact that both cases have the same kind of completeness and the same kind of incompleteness. You can explain a man's detention at Hanwell by an indifferent public by saying that it is the crucifixion of a god of whom the world is not worthy. The explanation does explain. Similarly you may explain the order in the universe by saying that all things, even the souls of men, are leaves inevitably unfolding on an utterly unconscious tree -- the blind destiny of matter. The explanation does explain, though not, of course, so completely as the madman's. But the point here is that the normal human mind not only objects to both, but feels to both the same objection. Its approximate statement is that if the man in Hanwell is the real God, he is not much of a god. And, similarly, if the cosmos of the materialist is the real cosmos, it is not much of a cosmos. The thing has shrunk. The deity is less divine than many men; and (according to Haeckel) the whole of life is something much more grey, narrow, and trivial than many separate aspects of it. The parts seem greater than the whole.

Chesterton - Orthodoxy, ch. II, The Maniac

https://freddoso.com//courses/439/orthodoxy2-3.htm

https://pubmed.ncbi.nlm.nih.gov/16079840/

Catastrophe theory; geniuses and maniacs (2011)