Paul Bettany believes that making a good movie is about guess work.

The British actor - who has starred in films including A Beautiful Mind, The Secret Lives of Bees and Iron Man - believes there is no guaranteed way to make a successful film, and he admits many people were surprised at the success of his latest work Margin Call.

"I've never seen more shocked faces. Because nobody could quite believe it had come together so well. I thought it was bright and well-written, which is rare, and it was 17 days of filming so I just thought, 'This is a good punt.' It's just proof that you never know. People are always trying to work out the formula for making a movie that is well-regarded, but it's like looking at f**king tea leaves."

Paul stars alongside Demi Moore, Zachary Quinto and Kevin Spacey in the movie, and he admits it "changed" him because it showed him how professional a set could be: "This movie changed me in that it reminded me of all the reasons why I first became an actor. I can't make movies that I don't care about any more."