The problem exists on both a micro and macro level. At the word-by-word end, you may edit a sentence or paragraph and replace it with what, at that moment, you think is better. Only later when you are thinking about it, in that obsessive way writers do, you decide you like the first way better. You return to the computer, and find it irrevocably gone. You try to recapture what you wrote, but the wording isn’t right. You blew it.
You have to get in the habit of creating a new file every time you revise. It seems like a pain, but you don’t have to copy and paste the entire manuscript. You start at the chapter heading (or even the top of the single page you want to edit) and drag the mouse to copy that section you know you’re working on. If you don’t want your manuscript file to get too cluttered, create sub-files (“Chapter X”). But don’t throw out your drafts until a much later date, when you’re sure you know what you want.
On a macro level, the danger can be that you lose material between drafts. Say, you write a scene for a murder, in draft #1. Yet when you read it over, you realize that circumstances impacting the murder changed. So you write a new scene that accommodates the changes. When you complete that draft, you’re reading it over and you realize that certain parts of version #1 were actually better, except for those few things you really needed to change. Only you can’t find the scene you wrote earlier.
Rather than reading pages upon pages in frustration, use the Compare Documents function in Microsoft Word. It asks for two files, so you put the original in one box and the latest draft in another. A third file emerges that shows only the changes between the two drafts. Now all you have to do is flip to the general section where the murder should be, and the highlighted text will jump out at you. (Note that you can also use this function for micro comparisons as well.)
“Put down everything that comes into your head and then you're a writer. But an author is one who can judge his own stuff's worth, without pity, and destroy most of it."
Copyright @ 2017, John Paine