The bit where you can’t proceed mentally with the story because you realized, 150 pages in, that you forgot to put in every major instance of foreshadowing and flashbacking that would have led up to your character doing the thing he’s about to do, so you go and start editing bits into the existing manuscript.
LOL, I need to stop procrastinating and get the rest of this plot banged out, seeing as I’m going to be doing heavy edits and additions no matter what I do.