I think present-day reason is an analogue of the flat earth of the medieval period. If you go too far beyond it you're presumed to fall off, into insanity. And people are very much afraid of that. I think this fear of insanity is comparable to the fear people once had of falling off the edge of the world. Or the fear of heretics. There's a very close analogue there.

Ch. 14 - Zen and the Art of Motorcycle Maintenance (1974)