Bloch’s novel focuses primarily on the character of Norman Bates, the “Aw, shucks” motel clerk who has something of a mother complex, and Stefano was sure that audiences wouldn’t want him to be the focus for the whole movie. So, what if instead, they didn’t introduce Norman until 20 minutes into the movie? As he told Cinefantastique:
“The idea suddenly struck me to begin with Marion, suggesting that the movie would be about a girl who steals $40,000. Audiences would be sucked into a character who did something wrong but was really a good person — they would feel as if they, not Marion, had stolen the $40,000. When she dies, the audience would be the victim! And that’s just how it worked. With so much early emphasis on Marion, no one dreams she’ll get killed. When it happens, people are blown away. It’s like Hitch and I were saying we’ve stolen your central character!”
This take intrigued Hitchcock and Stefano got the job. They both agreed in order to sell this conceit they would have to cast a star of some renown to really fool the audience, so they cast Janet Leigh, and that’s how we got one of the best gotchas in movie history.
By the way, the screenwriter still had reservations about Norman Bates as a character. He didn’t like him on the page, thinking he wasn’t likable enough to carry the twist. Hitchcock was already ahead of him on this point, though, and told him that the problem would be solved by casting and told Bloch to picture Tony Perkins. Stefano said, “I knew then I could write the character.”