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.

I don't believe in objectivity. I observe the observer's paradox every moment I'm filming. Your presence is changing everything; there's no mistaking it. And you have a responsibility.

With portable cameras and affordable data and non-linear digital editing, I think this is a golden age of documentary filmmaking. These new technologies mean we can make complicated, beautifully crafted and cinematic films about real-life stories.

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.

Extreme sports tricks are becoming increasingly complex, the courses ever more challenging and crashes all too common.

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 great locations in movies, and I couldn't believe I'd never seen a landfill on screen before. It was the most haunting place.