Everybody — okay, maybe nobody — understands that movies are not shot in the order we see them on the screen. Otherwise, why would we need editors, right?
Actually, movie directors shoot location by location with no respect for the chronology of the on-screen story. The end of the movie might be shot first, depending on where the scene occurs, which actors and actresses are available at the time, etc.
Given that, how does the movie maker ensure that the actors are wearing the same clothes and jewelry, the window in the set is open, etc., from day to day and week to week?
That’s the job of the film notetaker, the universal memory, the script supervisor. Formerly this person was known as the continuity girl because young women tended to hold this position.
This person is always on set, always taking notes on what everyone is seeing, saying and doing. Where is the actor looking? Which hand does the actress use to slap his face?
You’ve seen the continuity screw-ups. For instance, in the Arnold Schwarzenegger movie, The Commando, Arnie totally smashes up a yellow Porsche. A few scenes later, he drives it away. That’s a continuity flub, and you want to avoid them.
What do movies have to do with writing fiction? And especially non-fiction?
You need a continuity file, too.
What is the protagonist’s dog’s name? How did he get it? (You think you’re going to remember it three months, six months, a year into writing? Huh-uh. Nope. Not going to happen.)
As your characters change, you have to keep track of them. How can the hero pull the trigger in the climax … when the villain cut off his trigger finger during their first encounter? (That’s a little drastic, but it illustrates the point. [Just another terrible pun.])
Ditto for favorite restaurant, wine, sandwich, beer, car, computer game, etc.
Continuity is especially critical for books in a series, obviously.
So, the lesson here is: You gotta be your own continuity girl, because no one else can be.
In short, after you have taken notes and drawn up your outline, keep adding to your notes. You’ll thank yourself later.