One can sense Freud's dilemma. He claimed that the sense of fear they experience followed by a sense of calmness was an intense source of sexual pleasure. Such events comprise the only available material for psychoanalytic work.
Freud's discussion of adult sexual aberrations links them to unexpected or abnormal events during childhood. Freud observed that some of this individuals have always had this attraction since birth while others developed this "condition" after a certain trigger.
Freud also viewed sexuality as fluid and not fixed, thus it developed over the course of an individual's life. The third and last essay on the theory of sexuality, "The Transformations of Puberty", ties the sexual development of the adolescent with the events of his early childhood which produce his adult sexuality.
Freud himself admitted that this could create difficulties for the reader. The infant, due to the diverse and polyvalent character of erotogenic zones as invested by instinct and by the various means of gratification, may be characterized as possessing a "polymorphously perverse disposition.