In an interview with The Hollywood Reporter, the Golden Globe-nominated actor said he challenged himself to "a do or die" moment with the play in which he performed opposite Julia Roberts and Paul Rudd in 2006.
He said preparation for the part was "the hardest thing I've ever been through, by far."
"I remember thinking, 'If this doesn't work, maybe I'm not right for this business,'" he said.
His most recent project -- "Silver Linings Playbook," in which his character suffers from bipolar disease -- has earned him rave reviews from critics.
He's been nominated for Critics' Choice, Golden Globe, Indie Spirit and Satellite awards, and voted the year's best actor by the National Board of Review.
"This is the dream, of course, to be able to make movies with people like this," Cooper said. "And, in terms of the recognition, it's a wonderful feeling."