Oh it's real, I agree. What I meant by "fiction" is that the success of waterfall, and the specifics of how waterfall are implemented, is fictional. As in during the "delivery phase", it is found that requirements were missed and so people will retroactively act as if those requirements were actually in the "requirements phase" all along. I did a lot of government contract work and saw the insanity in action.

Lots of retroactive changing of gantt charts, too :)