As a writer, it’s important to me to create the best possible work I can. In order to do that, I need an objective pair of eyes to comb through the manuscript, picking out character agency, weak plot points, and grammar. There are methods for doing this yourself, but I don’t recommend it, as you may overlook details (or lack thereof) that someone else will find.
Whether it’s a novel, a script or a short story, every writer will create a not-so-great first draft. In order to shape it into something better, a writer then turns to an editor for assistance. In some cases, an editor can help with a story that has stalled out half way through.
When I was working on my current novel, I stalled out in the middle. I’d already cannibalized a short story into the novel, which gave it layers I hadn’t expected. However, I had no sense of what was going to happen next. There were a couple of scenes written out, but I had no idea of where to put them, and no clear, definitive, final wrap-up to the story.
I was stuck, in the truest sense of the word. I needed help. So I found an editor who helped to jump-start a new direction for the Narrator and the story itself. In two five-hour editing sessions, I had gotten past the block and found myself at the story’s end.
How did this happen? I set aside my ego and listened to what my editor had to say. There were points I didn’t necessarily agree with, which pushed me to find a way to make those points work within the story. If I was successful, they stayed in – if not, I ultimately took them out. It was a difficult thing to do, excising portions of my novel (particularly if it was a character I liked), but that’s what the sequel is for. 
Ultimately, as a writer, if I want my work to improve, I need to pay attention to my editor, who also acts as my mentor. The relationship between an editor and a writer is symbiotic – when the two click, the work is a joy (even if it’s still frustrating). When it doesn’t, thank the editor for their time and effort and look for someone with whom you can develop a long, professional relationship with.
Every experience with an editor, even one that doesn’t work out, is a positive one – it helps you focus on your work, your voice and your goal.
That goal? To hone your craft and create your best work.
 The character in question went through nine name changes and switched nationalities – if he hadn’t been so endearing, I’d have written him off long ago.