The 40-year-old, 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.
He says 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," femalefirst.co.uk quoted Bettany as saying.
"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 tea leaves," he said.
The actor stars alongside Demi Moore, Zachary Quinto and Kevin Spacey in "Margin Call".