" The points to be emphasised are, first, that Freud's psychical energy model originated outside psychoanalysis, and, secondly, that a main motive for his introducing it was in order to ensure that his psychology conformed to what he believed to be the best scientific ideas of the day. Nothing in his clinical observations required or even suggested such a model—as a reading of his early case studies shows. No doubt partly because Freud adhered to the model throughout his lifetime and partly because nothing compellingly better has been available most analysts have continued to employ it. "

― John Bowlby , Attachment