The film was based on screenwriter Rob Perez's own diary recounting his experience with self-denial, which Hartnett read to better understand what his character might be feeling. Hartnett's verdict? "Just madness!" So Perez didn't last through 40 days? "Are you kidding?"
[Hartnett himself conducted an experiment -- and lasted about two weeks. He was later asked what he would give up for Lent: "Something a lot simpler than sex," he said. "Pop or candy, or something like that."]