If this documentary is swift and witty, that’s in part because it relies heavily on clips of Orson Welles talking. And oh, how Welles could talk, that beautiful voice wrapping itself around tall tales and wine commercials with equal grace.

He made “Citizen Kane,” the greatest movie of all time (no matter what Sight & Sound says), and spent the rest of his life being asked why he couldn’t just up and make another. Many distinguished talking heads discuss the reasons. The movie is mostly on Welles’ side: It sees him as a maverick genius fated to butt heads with the suits, no matter what.

The clips of Welles’ movies (especially “Chimes at Midnight,” a great film kept unavailable by years of petty legal squabbles) show that whatever it was that kept him from the career he should have had, it was, and remains, our loss.