“Mommy and Daddy will be right next to you,” little Sammy Fabelman is assured at the beginning of The Fabelmans, Steven Spielberg’s exploration of the creative engine that has always driven his work, his parents’ divorce. That engine is quickly given metaphorical shape in the spectacular train wreck sequence of Cecil B. DeMille’s 1952 circus movie The Greatest Show on Earth, the first film Sammy, Spielberg’s alter ego, has ever seen. The cataclysmic crash has such a terrifying and awe-inspiring effect on Sammy that he feels compelled to re-create it by becoming a filmmaker. Advertisement One of the principal jobs...