The first edition of Psychopathology of Everyday Life of 1901 starts with Freud's surprising account how he detected the reason why his travel companion misquoted a line from Vergil's Aeneid. Freud claims that by way of a test game in which he applied his newly invented method of analyzing and interpreting dreams he traced the cause of the misquote to a hidden fear in his interlocutor's soul: the young man had to admit that he dreaded the possibility of having made his Italian girl friend pregnant.
In a just published essay (Freud's Aliquis-Anekdote, Sinn und Form 2020/3), I have assembled clues and evidence found earlier by Sebastiano Timpanaro, Richard A. Skues, Jeffrey M. Masson and Franz Maciejewski. Adding insights from my recent book on Freud's four major case histories (Freud's Phantasiestücke. Die Fallgeschichten Dora, Hans, Rattenmann, Wolfsmann. Oberhausen 2019) I have come to the conclusion that the aliquis episode never happened in reality but that Freud invented it, turning his own fear of having just fathered a very much unwanted child into a fictitious but brilliant "proof" of the efficacy of psychoanalysis.