The words you cut are the most important
A quick confession: On average, I end up cutting about 10% of my manuscript during the revision process. TEN PERCENT! Am I the only one that thinks this number seems huge? To put this in perspective, I'm nearly done revising Taken's sequel, and I've currently cut 14k (15%) from the story. With Taken, the novel shrunk by 11k (almost 9%) during editorial revisions. I guess I write rambling first drafts!
Despite the drastic changes in word count, I always find the shorter version of my story to be the richer version. The more layered, more intense, more emotionally charged. Even still, it's difficult to not cringe when I think about how much I write, only to later cut. It feels like a waste of time and energy. But the truth of the matter is this:
Overwriting initially helps ensure I understand my characters, their motives, and world. It is only after overwriting that I can pare back and effectively craft my tale for the reader.
I'm going to take a detour real quick. Bear with me...
I used to design websites for a living. Never, not even once, did I open Photoshop, spend a day designing, and have a finalized layout for a website. Not once did the first round of designs concepts get approved by the client. I always had to go back to the drawing board, always needed to tweak, layer, redesign, adjust, and improve upon the foundation.
This never boggled me. How could I possibly know exactly what the client/company wanted their website to look like on the first try? I expected to design only to delete. And then to design again, over and over until I laid the right foundation and trimmed away all the unnecessary flourishes. After all, one of the things I heard often in design school was that a good design exists when everything serves a purpose and nothing can be taken away.
This could not be more true with writing. In fact, the origins of this piece of advice comes from a writer:
Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away. —Antoine de Saint-Exupery
And this is why you shouldn't lament the words you cut and slash from your manuscript. It's the cutting that makes your story shine.[1. Obviously fixing plot holes, improving world-building, fleshing out character arcs, etc. are all incredibly important steps in the revising process as well. But when you reach the polishing stage, making sure every page on the word adds to the story, and that nothing can be removed, is critical.] Perhaps you needed to over-explain a world-building element before you could explain it simplistically (and in half the words). Maybe you had to do an awful lot of telling—paragraphs and paragraphs of it—before you trimmed back to the seemingly effortless showing. Or maybe you needed your characters to talk and ramble and internally-monologue before you realized their mere actions illustrated their feeling far more effectively.
You may have to do all that overwriting for yourself. You are trying to determine what's necessary and what's not. You're trying to understand every last detail of you story so that you can share the right details—the necessary ones—with your reader.
So revise, trim, pare back. And remember that all those cut words aren't a waste of time. They are just as important as the ones that exist in the final version of your story. They might even be the most important, seeing as they are the bridge that gets you to the good stuff.