Who in the rainbow can draw the line where the violet tint ends and the orange tint begins? Distinctly we see the difference of the colors, but where exactly does the one first blendingly enter into the other? So with sanity and insanity.

-Melville, Herman
Billy Budd, Foretopman (first published1924), ch.21.

   A genuine invention in the realm of ideas must first emerge as an abstruse and even partial concept† At first blusha new idea appearstobe verycloseto insanity because to be new it must reverse important basic beliefs and assumptions which, in turn, have been institutionalized and are administered by one or another kind of priesthood with a vested interest in an old idea.

-Miller, Arthur
  The Collected Plays,'Introduction, II'.

I have noticed again and again since I have been in the Churchthat lay interest in ecclesiastical matters is often a prelude to insanity.

-Waugh, Evelyn Arthur StJohn
  Decline and Fall, pt.1, ch.8.