From Robert Pirsig, LILA: An Inquiry Into Morals, 1991:
There was a famous experiment where a sane person went onto a ward disguised as insane. The staff never detected his act, but the other patients did. The patients saw that he was acting. The hospital staff, who were playing standard social roles of their own, couldn’t detect the difference.
Insanity as an absence of common characteristics is also demonstrated by the Rorschach ink-blot test for schizophrenia. In this test, randomly formed ink splotches are shown to the patient and he is asked what he sees. If he says, “I see a pretty lady with a flowering hat,” that is not a sign of schizophrenia. But if he says, “All I see is an ink-blot,” he is showing signs of schizophrenia. The person who responds with the most elaborate lie gets the highest score for sanity. The person who tells the absolute truth does not. Sanity is not truth. Sanity is conformity to what is socially expected. Truth is sometimes in conformity, sometimes not.