Ruffalo says that while he doesn't normally receive scripts that ask him to go this dark, the real appeal of this was the fact he's known Brian for seven years and that this was based on Brian's real life experiences. "The true story aspect of it makes it completely different," explained Ruffalo. "In my memory I can't remember a lot of films that are quite like this that deal with drug addiction and crime and then just rising out of it in a really kind of honest way. And, you know, it either glorifies it or it just gets so sappy with the like 12 step stuff that it becomes like a preachy kind of thing. I just felt like this told that story really simply, in kind of a '70s sort of nod to that time period of making films. It's a simple story that had great, you know, it had some guts in it. It had some moving stuff: family, redemption and all these interesting elements."
Amanda Peet co-stars as Stacy, Brian's long-suffering wife who stuck by him despite his many flaws. While Peet said she didn't want to delve too deeply into analyzing why Stacy remained loyal to Brian, Ruffalo said he normally does want answers to that sort of question. "I probably would tend to want to know, get a deeper cut on it. But in those seven years Brian and I became very good friends. I was going to do the movie in the beginning, but he couldn't get it made with me so I said, 'Listen man, go on and do this movie. You have to do this movie and I’m not going to impede it in any way.' But we remained friends, very, very close friends. And so during that time I just got to know the stories intimately and so I knew what their relationship was and what drew them together," revealed Ruffalo. "You know, they're that young couple who starts off like, a lot of it is hormones and like sexual attraction and her caring for him, setting up his bed, and all those things. But then they throw themselves together because their families’ lives are so bad. And it just becomes messy, and then 10 years later they're two totally different people."
Not only did Ruffalo have to get into the character of a low-level criminal drug addict, he also had to tackle a Boston accent. That initially worried him until Goodman gave him very specific advice. "I kept saying to Brian, 'Brian, man, I need to get a Boston…I need an accent coach.' And he’s like, 'No, you don’t. No. None of that sh-t, no, no.' He’s like, 'The Boston accent is, if you hear it in a movie it’s too much, right?' He just hated it and he really doesn’t like it in movies and he was very, very adamantly very opposed to it. But what I did was just like, what I did is I actually videotaped about a 30-second clip of him speaking and then memorized that and got all the sounds pretty close to that. And I would just keep referencing back to that. And then he would come up to me like, 'Dude, that sound, that word’s not like that at all.' And then the other thing you want to do is like kind of get this tough guy, clenched fists. He's like, 'Don’t. Don’t do that.' But he would catch me and give me adjustments along the way, but I was just playing him really."
As for the playing a drug addict, Ruffalo joked about his research process. "I went out and got like an eight ball and," said Ruffalo, laughing. "No, I’ll never forget when I showed up there and one of the guys was like, 'Hey Mark!' And I was like, 'Yeah?' And he's like, 'Let’s go hit some crack houses. I know a couple.' You know, one of the actors in the movie, right? And I was like, 'Yes, let’s do that,' and he's like, 'Seriously?'"
"You know, it’s like addiction, I have a saying – either you are one or you love one. And I’m not. I don’t have that gene or whatever, but I have a lot of people in my life that do unfortunately. And I've seen people doing it. I know people that I'm very close to who are in the clutches of that. You know, part of probably why this movie meant so much to me was to be able to tell that story in a way that there was some like rising above it. And then Brian just like sat me down with like a couple of Altoids and we chopped those babies up, threw them in the pipe and he showed what it looked like. He showed me and it was interesting to watch because, you know, he hasn’t visited that world in many, many years. He became almost physically ill. That scene when [Ethan Hawke] finds me, [Brian] was like, he was ruined. He couldn't even call a cut. It was a very intense day."
As difficult as some scenes were to get through, Ruffalo believes writing and directing What Doesn't Kill You was very cathartic for Goodman. "He’s writing it, he’s doing those things, I think he started to write it out of making amends - like taking account of his life. And so he’s writing it, but the day when we’re there and is ex is there, his real ex is on set and his kids are there and the scene’s playing out in front of them, it just knocked him down. He got it. I mean he got it from her point of view."
"There was a phone call [scene] where I'm like, 'Leave me the f--k alone!’ He couldn’t call cut and he was back there weeping. And it was really personal and intense, and it takes an enormous amount of courage to be that honest with yourself and then with the world about yourself. That's a real reckoning and I don’t think you can do it without doing that in a way. He’s kind of a hero to me because very few people that I know can be that honest about themselves and their shortcomings, and so I just felt deeply responsible to go to those places honestly and tell those stories. But all that said, there's a lot of love there. It was a very, very special shoot. I don’t know if it translates or not, but it was just one of those very, very special movies for the people involved. You felt the gravity of it, but you were also being buoyed by the healing nature of it too. That's what kept us from just falling into the abyss."
