they never understood the book, either, although the book sides more with the "reject your capitalist-fueled slavery and find freedom in spewing testosterone out of every pore" anarchy angle than fincher's "life isn't defined by your acceptance or rejection of modern society, and self-satisfaction lies in choosing your battles" message. Palahniuk, being the hack he is, got so enamored of all the praise from his bareknuckle teenboy fans that he's taken up the pro-anarchy interpretation of the book, making it canon.
the book is one of the atlus shrugged flashpoint texts, because it manages to encapsulate a certain type of social dissatisfaction -- as is appropos of most quasi-religious tracts. as a result, it has its creepy-ass faithful who regurgitate their half-baked interpretation of it in all-too-many venues, and have gained the book far more notoriety than its pseudo-intellectualism deserves.