A man like me cannot live without a hobby-horse, a consuming passion — in Schiller's words a tyrant. I have found my tyrant, and in his service I know no limits. My tyrant is psychology. it has always been my distant, beckoning goal and now since I have hit upon the neuroses, it has come so much the nearer.

Letter to William Fless (1895), as quoted in Journal of the History of the Behavioral Sciences Vol 3-4 (1967) p. 159