Half a century ago Maudsley wrote “A pregnant but very difficult question of which little or no thought has ever been taken by writers on insanity is—What is the cause of the particular form which the disorder takes in a given case? Why does it assume one complexion rather than another? At the outset it is certain that what appears to be the same cause shall occasion different forms of insanity in different persons and even in the same person at different periods of life, and that the same form of disorder shall be produced by different causes; this being so it is plain that the special determining conditions lie hidden in that unknown region which we call by such names as ‘temperament’ and ‘idiosyncrasy.’”