Lost in La Mancha, a 2002 documentary about a film that ending up taking over a decade to finish after a doomed first attempt narrated by Jeff Bridges (The Big Lebowski).
This film is "The Man Who Killed Don Quixote" directed by Terry Gilliam. While Gilliam had a seemingly massive budget of $32m his uncompromising vision meant that to make the movie almost no mistakes could be made with the money he had. Will his plan succeed?