On Honey Boy, director Alma Har’el waded through “a burning mist of pain” to hit upon the raw truth she says she values most. Coming to her via Shia Labeouf—who began writing the script in court-ordered therapy—the film examines the turbulent coming of age of an actor estranged from his father. From the beginning, Har’el saw a story that could speak powerfully to the therapeutic value of art. But to tell it with emotional authenticity, she would have to convince her frequent collaborator to do the unthinkable: to revisit his traumatic past, from the perspective of his abuser.

Deadline: You stood by Shia Labeouf at a life in his life when no one else would. Why do you think that is?

Alma Har’El: I think that growing up with a lot of addiction around me—alcoholism, mental health issues, things like that—has given me the...