The idea for the film came from Joaquin Phoenix's amazement at the way people believed that reality television shows were unscripted. By claiming to retire from acting, he and his brother-in-law Casey Affleck planned to make a film that "explored celebrity, and explored the relationship between the media and the consumers, and the celebrities themselves".
The first hint that Joaquin Phoenix was going to pull a stunt like this came in October 2008, when he announced his retirement on the red carpet of his film Two Lovers (2008), which he then proclaimed to be his final performance. (Ironically, Phoenix got some of the best reviews of his career for his performance in the film.)
Phoenix originally conceived of the idea after he became fascinated by the show Celebrity Rehab with Dr. Drew, and in fact, originally attempted to execute the stunt by being featured on the show. However, Phoenix ditched this idea, when he realized it would be cruel to be performing a character amongst people with very real problems.
In September 2010, co-screenwriter and director Casey Affleck confirmed that this movie is not a real documentary, but fake. The public had been wondering ever since Joaquin Phoenix announced in October 2008 his retirement from acting, in order to become a rapper, whether it was all just an act or if it was for real.