In “Orthodoxy,” G.K. Chesterton explains that madness is not a lack of rationality, as we typically think, but more often an excess of it. He uses the example of a man who believes that everyone is conspiring against him. For every argument you might make against his being the object of some vast plot, the madman will have a response that is perfectly consistent within his theory about the world. You might point out how the store clerk didn’t know who he was and, therefore, could not be conspiring against him, but he would only say the clerk was just pretending not to know him, as one would do if they were conspiring.
The problem, Chesterton points out, is not with the consistency of his arguments, but with the smallness of a world that could be so easily explained. Reason, in this sense, is not a way of making connections about the world, but a way of fitting everything in the world into one explanation.
“I admit that your explanation explains a great deal,” Chesterton writes of the madman, “but what a great deal it leaves out! Are there no other stories in the world but yours; and are all men busy with your business?”