The lunatic is the man who lives in a small world but thinks it is a large one; he is the man who lives in a tenth of the truth, and thinks it is the whole. The madman cannot conceive any cosmos outside a certain tale or conspiracy or vision.
Source: Charles Dickens, Dickens and America (1906).
-- G K Chesterton, (May 29 1874-1936), English essayist, novelist, journalist, poet; He is noted for the detective series with sleuth Father Brown.