EXCLUSIVE: With its billion-dollar business and dark subversive spirit, Todd Phillips’ Joker has been, fittingly, the wild card of superhero cinema this year, and the Warner Bros film’s compelling success began with the boldly off-kilter screenplay by Phillips and Scott Silver.

Phillips is best known for the audacious Hangover films, but with the Joker script he and Silver pressed into the psychological recesses of modern life and found their disaffected central subject in Arthur Fleck (Joaquin Phoenix), who veers from the traditional comic book portrayals of the Gotham City madman known as the Joker.

Joker bucks the traditions of DC Comics and also rebels against the brightly lit storytelling of contemporary superhero films, which tend to over-explain every corner of their characters. “We purposely set out to leave some things vague and unanswered,” Phillips said. “That was a clear intent from the beginning.”

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The reaction to the movie has been varied and intense and its controversies are well documented, but for Phillips the most intriguing feedback has been concerning a single line in the script.

“I think a lot of different things about the film have really connected with people and one of the things I’ve noticed has really caught on is the idea of what Arthur writes in his notebook: ‘The worst part of a mental illness is that people expect you to behave as if you don’t.’ That really resonated with a lot of people who do suffer from mental illness and saw a little bit of themselves in the movie, or in Arthur, or in his experiences in different ways. I’ve had so many people write me emails or posts on my Instagram saying, ‘That line is exactly what it feels like…’ “

Phillips said a hospital patient with a plaster cast or a neckbrace isn’t expected to disguise their symptoms or hide their hurting, but a different standard applies in the psychiatric ward.

“If you have a broken leg people hold the door open for you and you clearly have an ailment, but when you have a mental illness it’s a hidden thing so even when people know you have it they just expect you to behave as if you don’t. They don’t see it on you and often they don’t see you at all.”

Read the screenplay here.