In the original novel the fact that Durden is actually 'Jack ' isn 't foreshadowed very well, however the film uses it 's medium as a visual art to foreshadow the eventual outcome far better than the novel. In the original novel the first time we see Durden is when he and 'Jack ' meet on a beach because Durden is building something that casts a shadow over where 'Jack ' was sitting. In the film, however, there are very brief flashes of Durden appearing on screen lasting for no more than frame before disappearing, and 'Jack 's ' first meeting with Durden is on a plane when the two discover they both have the same briefcase. Other clues to Durden 's that were absent from the book but present in the film are little hints; Such as a man moving out of 'Jack 's ' way on a bus, but not Durden 's, or during a scene in which 'Jack ' is beating himself up in order to blackmail his boss, 'Jack ' notes that beating himself up reminds him of “For some reason, this reminds me of the first time I fought Tyler”
The major difference between the film and the novel is the ending. In the ending to Chuck Palahniuk 's original novel, Durden 's plan is to let himself be martyrd inside the building Project Mayhem intends to destroy. 'Jack ' discovers that he and Durden are the same person and Durden 's plan fails, and the building remains standing. 'Jack ' decides to end Durden and shoots himself