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 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.

Why is nobody questioning the sanity or suicidal tendencies of Everest ascenders? It's kind of a question of framing: How do you frame these activities? We frame them as freedom-loving, exciting, progressing sports and they are. But there are other ways to frame it. It's also true that these young men, neurologists say that their frontal lobes aren't developed yet - the long-term planning part of the brain.

I think we've reached that point where we understand medically what we are doing to ourselves with these sports. In football, it's kind of hard to get the access that you want for the story and, of course, it's very long-term: the effects of the repeat concussions really don't hit until decades afterwards, whereas the traumatic injuries in extreme sports are very immediate. I realized Traumatic Brain Injury was a fascinating and important story that not had been told very much. I wanted to know more.

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 find titles the hardest thing. I was worried that 'Waste Land' was too much of a downer. For me, 'The Crash Reel' confronts what the film is about: it's not just about the reality of a crash, it's about the extremity we all face, and what happens when life crashes on you.

I remember when the Berlin Wall fell and suddenly intractable problems get solved.