Rob Burnett made his first break interning for David Letterman in 1985. Working his way up to head writer of Late Show with David Letterman in 1992, he eventually became executive producer. After more than twenty years in television comedy and multiple Emmys, he's on his way to the same success in film, writing and directing the charming and funny Sundance closing-night hit - and now Netflix Original film - The Fundamentals of Caring.

Based on the novel by Johnathan Evison, The Fundamentals of Caring stars Paul Rudd as Ben, a father grieving his tragically lost son, who, in desperation, dives into caregiving for Trevor, played by Craig Roberts, a teenager with Duchenne Muscular Dystrophy.

I sat down with Rob Burnett at the 70th Edinburgh International Film Festival, where the film had its European premiere, to ask him about working with Rudd and Roberts, making death and disability funny, and why he chose Netflix to distribute the film.

What first attracted you to the material?

The traditional story that I've seen in this regard is generally an ill or injured person, and an irascible caregiver comes in and breathes life back into the person. That's been done to great effect before. In this, Ben (Paul Rudd) is every bit as damaged as Trevor (Craig Roberts). Neither of them are going to get better, neither of them are particularly interested in helping one another - at least in the beginning. So, there's just something so lovely about that - that bond and the tiniest bit of growth for the two of them.

One of the challenges in writing and directing this movie is that they're never going to get better. You're not writing a movie where the guy wants to become heavy-weight champ and then, by the end, he makes it. Ben's never going to get over the loss of a child - I have three kids, I'd never get over that, I don't think anyone ever does - and Trevor's never going to get out of that wheelchair. So, how do you make a movie out of that? And yet, I think there is something incredibly inspirational about these guys, both literally and metaphorically, getting out of the house. Letting life in just this much. I find that very dramatic and moving in the smallness, that in some ways extends out for all of us. It's not a long leap to say we're all kind of dying every day. What more do we have but to go out and try to do all these little things, because that's all life is. It celebrates the smallness, I think.

There's a lot of jokes about upsetting subject matter and realities of disability in the film, but it doesn't feel like poking fun. How important was it to you to get that right?

One of the best things, for me, was when we went to Sundance. There's this guy called Case Levenson, who has Duchenne muscular dystrophy, he was the original inspiration - he's the real life Trevor. Johnathan Evison was actually his caregiver. Case and his mom, who is his primary caregiver, came to our premiere at Sundance and I was nervous and interested to see how they would react to the film. Case's mom hugged me after the movie, they both loved the film.

It meant so much to me that they loved it. 

A woman named Tracy Seckler who runs Charley's Fund - a big DMD charity in New York - acted a little bit as a consultant on the film. I would call her and ask technical questions, and she set up kids with DMD for Craig and I to meet, just to try and get it right. She also adored the film, and what came through - the reason they loved the movie - is that Trevor is a character. He has Duchenne muscular dystrophy, but he's not defined by it, you know? He's a character who happens to have this disease, and I think this is the thing that everyone responded to. That is what I was going for.

Some of the inspiration for this was a childhood friend. A friend of mine, who I knew since I was six-years-old, unfortunately passed away from ALS about seven years ago. It was the first time that I'd ever seen a disease up close. To be with him and see it on a day-to-day basis - if you know about ALS, the mind is fine but the body is going away - and my buddy is this lovely, funny, hilarious guy. I still just saw this guy, because I'd known him my whole life. If you'd seen him, you might just see a guy in a wheelchair and categorise that in a certain way, but for me, he was just categorised as this great man, that I'd known my whole life. That is something I, very definitely, wanted to bring to this film. I think these are the things that Tracy and Case's mom responded to. You don't have to look at a person in a wheelchair and put them in that compartment in your head. They can be funny, they can be mean.

One of my favourite lines in the movie is when Trevor says, "have you ever thought that maybe I'm a prick with or without the wheelchair." Tracy said to me that, by the end, you forget he's in a wheelchair. I've had more than one person say that. So that's super satisfying to me. To be able to treat these guys as guys, with moods. They're funny - they're this, they're that - and yes, they've suffered this tragedy. So, okay, these are the cards they've been dealt, but they're going to go on and live their lives. For these guys, humour is their thing, and by the time you get to the point where Ben can make a joke about muscular dystrophy - the fact that they're that comfortable with each other - that's beautiful. That's the way to bond those guys, more than sitting them down and have them say, "So, how does it feel to be in a wheelchair?"

The chemistry between Paul Rudd and Craig Roberts is very important to the film, was that apparent from the start?

I think the chemistry between Paul and Craig is the entire movie, because it's such a slight story really. It's really just about these two characters who manage to breathe a little bit of life into each other, who at the beginning have no interest in doing so.

I'd been sent books by my agency in order to adapt one to a screenplay, Jonathan Evison's was the first one I got - and I loved it! When I told the agency I wanted to buy the rights to the novel, there was just silence on the other end. 'Oh, so the one you want to turn into a movie is the one where a guy who's grieving goes to take care of a kid in a wheelchair. That's what you think will be a hit'. I never thought this would become a film, it didn't seem commercial, but there was something about it that resonated with me. Then I went to Paul, and that's where it all happened. Amazingly, Paul responded to the script and said that he would do it. Once Paul is in your movie, then finance comes and everybody wants the part of Trevor. We went through 250 auditions to get it down to about three or four actors. The minute I saw Paul and Craig together, I knew. They made it all very easy for me.

My sensibility as a writer and director is never to push things out and make them wacky, and the material here is so delicate that it has to be played so that you don't lean into it. If you're leaning into it, it'll just disintegrate in your hands. Craig has a natural instinct to not lean into things. The other young actors we saw were good, but you just know as a director that you'll just be pulling them back every day on set, which is tough on a twenty-three day shoot. I've watched this movie now more than any human should see any movie. Of course, I'm tired of all my dialogue, but what I really love to watch is just Paul and Craig.

I found myself relaxing into the film early on, when you get the banter between Rudd and Roberts. It gets emotional and it gets more serious, but eases you into it.

That's exactly the experience watching the movie with audiences. Generally, when Trevor first comes in, you can feel people recede and get nervous, because he's grunting and playing up the idea of being disabled. But, the minute they realise he's kidding, there's a release. And when Trevor asks how well Paul would wipe his ass, and Paul says "I'd wipe your ass so that there'd be no shit left on it", there's a huge release and then off you go! You either want to watch these guys for 93 minutes or you don't, and I knew going in that's what would eventually make this movie succeed or fail. And if it is succeeding, it really is Paul and Craig.

Roberts is restricted in his performance by the physical realities of muscular dystrophy, how did you work with him to realise that?

The brilliance of Craig is that he gives you so much while doing so little. Craig is just unbelievable in this movie, I can't wait for people to see him. In every frame of this movie, when you watch Craig, there is a natural sadness that is just right underneath everything else he's doing. He's witty, he's sarcastic, sometimes mean, but there is a deep sadness under all that, that is always present in his eyes. It draws you in and makes the movie.

Roadside attractions feature heavily in the film. Is that a metaphor for these two guys?

Yes, absolutely. No one really enjoys roadside attractions - you enjoy them ironically. It's a very detached enjoyment. I thought it would be nice if, at the end, the hidden beauty of something would come through. For Trevor, everything is at a distance - life is dumb, life is stupid. It's a safety net, it's an armour. That's really what this movie is - bit by bit that armour comes down for both of them.

I also tried to use windows through the movie as a metaphor. There's this window between them and the world. These are all things that, even if the audience doesn't notice them astutely, I do think they have an effect nonetheless. They go inside people, even if they aren't fully aware of them.

What's the reaction been so far from audiences?

I don't know how to say this without sounding ridiculous. In Sundance, the response was incredible. It was thrilling for me. I give all the credit to the actors. I think the movie is very playable. There are different kinds of movies. Some are more challenging - and I think they're beautiful for that - this movie is more friendly to audiences. I think it's an easy movie to watch, it's paced quickly, there's big laughs - that's something I'm very proud of.

Most dramas that are funny, the laughs are amusing or delightful - they make you smile and feel warm. But, as I said to Paul Rudd at the beginning, I think we can get big laughs - and, based on the screenings, we have. And it never gets outside of itself - there's no one getting kicked in the nuts in this movie. It all stays on the smallness of the characters, but its hooked up in a way - and, again, I give all the credit to Paul, Craig and Selena - that people seem to be responding to it.

Netflix bought all the release rights for the film, what was it that made them so attractive?

They've been amazing, they loved it straight away. First, they bought the streaming rights, then they came back and made it a Netflix Original - which, in today's world, is a real honour. It's what having a TV show on HBO had been.

It's such a different model. They don't need to worry about getting people to come opening weekend. Netflix understands it for what it is. I think they're maybe a little less scared about trying to market a movie with a kid in a wheelchair, they look at the bigger picture - here's a movie that people are loving, and hopefully based on the playability will have great word of mouth. They can be a bit more patient than a theatrical release, where you've got to market it, market it, market it - get everybody in on the first weekend or else you're gonna die.

This is a very intimate movie. Yes, I'm a director, so I want my work playing on giant screens because we're all idiots - it's what we do. But, unlike one of these giant, epic movies, if I'm honest about it, this movie plays beautifully on a small screen. From my standpoint, as a filmmaker, the idea that we can be in 190 countries, in front of 81 million subscribers, in 12 languages - on a single day - is beyond anything my tiny, grape-sized brain could imagine.

The Fundamentals of Caring is available now to stream on Netflix.