by Chris Bodenner
A reader writes:
One day, while he's lying sick in bed, Cameron lets "Ferris" steal his father's car and take the day off, and as Cameron wanders around the city, all of his interactions with Ferris and Sloane, and all the impossible hijinks, are all just played out in his head. This is part of the reason why the "three" characters can see so much of Chicago in less than one day - Cameron is alone, just imagining it all. Here's a more detailed explanation from Cracked:
Cameron creates Ferris in his mind. Ferris is the total opposite of Cameron: he's fun, spontaneous and has a loving family and foxy girlfriend. At the beginning of the film, the imaginary Ferris convinces a bed-ridden Cameron to "borrow" his dad's Ferrari 250 GT California and cruise all over Chicago. Given Cameron's crushing social incompetence, it's likely that Sloane is fictional too and represents a girl that he has a crush on.
This theory explains the more fantastic elements of the film. For example, the whole city of Chicago rallies around the "sick" Ferris. This represents Cameron's miserable home life and how he yearns for friends and family who give a shit. Or, perhaps Bueller is a guy Cameron knows but isn't friends with, and his fantasy is based on what he imagines life to be like for the "popular" kids at school--everything is easy and the world revolves around them.
When Cameron accidentally trashes his father's Ferrari at the film's climax, he realizes that he needs to stick up to his father and take responsibility for his own life. At this point he "disposes" of Ferris and Sloane. Both of his fictional friends receive happy endings: Sloane is left pondering marrying Ferris, whereas Ferris safely returns home, where he can break the fourth wall for eternity.
Derek James covers five more "Insane Fan Theories That Actually Make Great Movies Better".