The cast of HBO miniseries “I Know This Much Is True” joined the Variety Streaming Room for a Q&A moderated by Variety‘s Cynthia Littleton on June 17.

Writer and director Derek Cianfrance, executive producer and star Mark Ruffalo, and cast members Kathryn Hahn, Rosie O’Donnell, John Procaccino, Philip Ettinger and Archie Panjabi discussed the generosity on set, handling emotionally difficult scenes and how they achieved the show’s incredible authenticity.

“All I can say is that this was one of the greatest experiences I’ve ever had as an actor, as a filmmaker, with this group of people who brought so much of themselves and the dignity and the grace in their own beings, their own experience, their lived experience to this project,” Ruffalo said.

Based on the 1998 novel of the same name by Wally Lamb, “I Know This Much Is True” follows identical twin brothers, Dominick and Thomas Birdsey, the latter of which is a paranoid schizophrenic who has been in and out of mental hospitals for most of his adult life. As Dominick attempts to get Thomas out of an asylum, he relives their relationship and the family trauma they both endured.

With the subject matter came an intense artistic environment. In order to let the actors flourish, Cianfrance said he encouraged them to draw on their own personal family issues and lead with their instincts instead of closely following a script.

“The instigation I gave to all the actors is like, make it alive, make it real, make it true, make it messy, get it wrong, because maybe the wrong is going to be what I use,” Cianfrance said. “Maybe, you know, let’s not try to play for results. Let’s try to play for the pureness of the experiment.”