The nice thing about having knowlegeable people around when you're editing or revising something is that you can enslave them as fact-checkers and constantly holler "Do drug dealers measure out weed with a scale or a ruler?" or "Would mixing baking soda with helium *really* create an anti-gravity wonder fluid?" or "Is it plausible for my character to choke on a credit card?"
Revision is a time for making sure the physics and chemistry of your world are sound, that you haven't completely botched the slang of whatever underworld you're trying to portray, and that you haven't confused hepatitis with haemophilia.
INTERN has seen some embarassing mistakes. Doctor characters who take someone's temperature to see if they have epilepsy. Fir trees whose "leaves" turn "brilliant orange" in the fall. Improper use of the word "do-rag".
This is the easy kind of fact-checking: the kind you can do on the subway, merely by polling wise-looking travelers and trying to read Wikipedia on your cell phone.
The more challenging (and painful) kind of fact-checking involves your characters' emotions.
"Would my main character really feel satisfied when her mean neighbor's house burned down, or would she feel lingering regret?" "Maybe I need to change how Ebenezer feels in that scene where he makes out with Britney, since I added that new scene before it where she reveals her base digust for him."
Too often, revision only consists of adding new scenes without adjusting existing scenes to account for the changed dynamic. It's like taking a go-kart, adding an extra wheel, and then expecting it to run the same way.
A little emotional fact checking can fix this:
In Draft 1, Ebenezer is overjoyed to be making out with Britney. In Draft 2 (now that we've added that extra scene) we realize that our Ebenezer can't possibly feel overjoyed—now he feels used or humiliated or angry-yet-lustful. If the Britney-Ebenezer makeout scene doesn't get revised, the manuscript stops making emotional sense.
INTERN suspects that the reason many emotional inconsistencies stay put in manuscripts instead of getting revised is because old scenes can start to feel like they're set in stone, and somehow "meant" to be how they are. In fact, old scenes are the ones that most need to flex, or even get cut, because the characters they portray are no longer the real characters in the book.
Now that INTERN is reading this over, it sounds kind of obvious. If this were a novel, INTERN would have to go back and revise the end of this post to reflect her authentic emotional state of fretful perfectionism. Since this is not a novel, INTERN is going to finish this post exactly how she planned to: