10. Everyone Is Dead
We'll start with the bush league crazy fan theories. Which sounds a little trivial given we're gonna be talking about theories wherein people think at least some if not all the characters in a movie are secretly dead, but it's become such a cliche that you can apply the thinking to pretty much any film and have it make sense. The kernel of the concept is rooted in Ambrose Bierce's 1890 short story An Occurrence at Owl Creek Bridge, otherwise known by the much more spoilery title of "A Dead Man's Dream". Set in the American Civil War, the story details the trial of a a Confederate sympathiser who is condemned to death by hanging. Something goes wrong, however, and the rope snaps, allowing the soldier to escape from his fate, rushing through the swamps and woods surrounding the titular bridge.
A bunch of weird, wacky and inexplicable things happen to him, right up until the twist ending that reveals the whole story was happening in his head at the moment of his death. It was all just the imagination of a dying man. Not quite the "it was all a dream!" cop out, but close. Some of the more morbid movie fans out there have applied this basic structure to countless films over the years, with claims as varied as the larger-than-life musical numbers of Grease all existing in Sandy's heaven after she drowned (as recounted in the song Summer Nights) to the Ghostbusters passing away following the climactic crossing of the streams, with the celebratory credits sequence that follows being posthumous. Which is quite the downer. Almost as bad as when you see all of them smoking and it breaks your six-year-old heart. Just us?