This is an anticlimax taken almost to the point of parody.
For thoughtful viewers, however, an equal surprise is still waiting. That is the mystery of why Hitchcock marred the ending of a masterpiece with a sequence that is grotesquely out of place. After the murders have been solved, there is an inexplicable scene during which a long-winded psychiatrist ( Simon Oakland) lectures the assembled survivors on the causes of Norman’s psychopathic behavior. This is an anticlimax taken almost to the point of parody.