Editors are human beings.
I know, it's a huge shock to us all, but they really are. Something we have to keep in mind going into edit letters, feedback and all of the wonderful things that can come from those things is that editors are human beings. Highly skilled, technically knowledgeable, human beings ready to whip your book into shape.
And sometimes, they are wrong. Now, I don't mean for you to take away from this the idea that you should ignore your editors or that it's all right for you to ignore every piece of feedback that they give you. What I suggest that you do, is talk to them. If there's a piece of feedback that, after you've sit with it, marinated with it, wrestled and worried over (And yes, you do need to let it marinate for a while. Just because you don't initially agree, just because you may feel like you got punched in the gut, doesn't really mean they were wrong), does not make sense, then you need to open up dialogue with your editor.
Perchance you thought you were writing in omniscient third and your editor comes back with edits for close-alternating-third on your entire manuscript...Well, it's time to A, consider that you weren't as effective in your omniscient third as you thought and B, to TALK to your editor.
Feedback is not a one-way-street. It is a dialogue between you and the people you are working with. Moreover, you will find that different publishing houses have different "house styles", and they'll want you to fit in with that style. This can be as basic as how you spell the word grey, to as extensive as the percentage of the book your romantic subplot takes up.
You have to know, going in, what the expectations are and you have to know your book. There will always be elements of any story that shifted left or right will make it stand out far more than it did before. Elements that don't change the core of your story. But you have to know what that core is. You have to know what you're willing to change and what you aren't--and why.
And you really have to ask yourself why. If you're really attached to Greg's hair being green...well, why? Why does Xander die? Why does Lulu fall for Steve? These sorts of things can be malleable, while say, your gay main character being gay is not. While querying some years ago I did actually run into an agent who told me she wouldn't be able to sell my book because my MC was bisexual. More importantly, because he had a male love interest.
If an editor had told me to change that aspect of the book to make it saleable, I would have walked away.
It was my line in the sand.
Try to remember though, don't draw your line in the sand in front of something that isn't actually critical to the core of the story. Learning to see the difference between the core and the malleable elements will make you a better writer and learning to talk to your editor, mentor, critique partner will definitely make you a better writer.
Ask questions, make mistakes, get messy...)don't get in a yellow school bus with a woman who has a pet iguana that actually drives the school bus.)
You will get suggestions you don't use--and you better have an explanation (a good one) as to why you didn't think the change was necessary, warranted, etc. You cannot say, "Because I didn't want to." it will not fly.
Bottom line, talk to your editor. You'll be happy you did.