I have always been interested in garbage: What it says about us. What in there embarrasses us, and what we can't bear to part with. Where it goes and how much of it there is. How it endures. What it might be like to work with it every day.

I can ask someone to let me into all aspects of their life for several years, but people have got to have that gift: that courage and that talent for opening their lives to the camera. Being candid is a gift, and that's what the audience responds to. Part of it is me asking, and part of it is just their inherent talent, which is what you are looking for when you make documentaries - people that are really going to let you in on what they are going through.

I am riveted by extreme sports like big-wave surfing, 'megaramp' skateboarding and half pipe snowboarding. I am fascinated partly because the sports are so exhilaratingly acrobatic. But I am also captivated by the fear that a terrible accident might happen at any moment. And accidents do happen.

I love my work, apart from when it's driving me crazy. But I get to be interested in stuff and think like a filmmaker as I'm buzzing about the world and then see an opportunity to make a film, and then make it happen.

I'm not an expert on how to configure the sport, but I can observe and say that accidents seem to be a part of it. The athletes are incredible, with the courage that they accept the risk of death, paralysis, and brain injury. These are really life-changing, life-threatening injuries, and the risk is extremely high.

There's a theory of accidents that I studied when I was making a film about nuclear weapons: you can never eliminate accidents, because the measures you introduce to prevent accidents actually produce more accidents. That's certainly true of this sport; you're flying over 40 feet of what might look like snow, but it's hard as ice, it's as hard as pavement. You're doing acrobatic spins and tricks, 40 feet above pavement, essentially. There's been more accidents since, and there are going to continue to be more accidents, that's the nature of the sport.

My main trick is to work with amazing people. It's a long and twisty journey and you need people that really are amazing and have this rare gift of honesty and courage and really open up.