" Freud only rarely draws on the data of direct observation, one or two of the occasions when he does so are key ones. Instances are the cotton-reel incident on which he bases much of his argument in Beyond the Pleasure Principle (S.E., 18, pp. 14–16), and the agonising reappraisal of the theory of anxiety that he undertakes in Inhibitions, Symptoms and Anxiety (1926). "

― John Bowlby , Attachment