“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 especially 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.
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 lunatics’ theory explains a large number of things, but it does not explain them in a large way.
The madman is not the man who has lost his reason. The madman is the man who has lost everything except his reason.”
– GK Chesterton (Orthodoxy)