One iteration of this trope has it that Steve Buscemi’s Donny from The Big Lebowskiwas really a ghost that fought alongside John Goodman’s character, Walter, in Vietnam.
If this theory contributed anything worthwhile or showed us a different way of looking at Walter, maybe we’d be willing to try and overlook the fact that multiple people interact with Donny in the movie. Unlike Cameron, however, Walter is far from self-loathing. Unlike the narrator from Fight Club, he is anything but repressed. The biggest problem with the “Tyler Durden” is the fact that it’s often shoved into a story with little thought as to the circumstances. Before you can add in a proper Tyler Durden, the character has to need a Tyler Durden.
The theory has been plugged into everything from Garfield to Rugrats and even back into Fight Club, which is about as arbitrary as theorizing that Tom Hanks was simply imagining Wilson the whole time.