Fifty years ago this week, director Brian De Palma had his first legitimate mainstream hit with “Obsession.” When “Obsession” came out, Schrader was just on the cusp of becoming one of the most celebrated screenwriters of his generation. ‘Obsession’ Courtesy Everett Collection“ I had written ‘Taxi Driver’ essentially as self-therapy, and then this weird thing happened,” Schrader told IndieWire. Had De Palma been faithful to Schrader’s original script, “Obsession” would have differentiated itself from “Vertigo” more dramatically; Schrader wrote an entire third act that De Palma never shot, softening what Schrader intended to be a portrait of all-consuming obsession. When Schrader saw “Obsession” as De Palma made it, his reaction was closer to Kael’s than Ebert’s.