What do you mean? How can my wondrous, amazing and brilliant work of art possibly contain anything even resembling a flaw?
Oh my god! They finally figured out I'm a complete fraud who doesn't know what I'm doing. It's only a matter of time before my story is revealed as the garbage I was always afraid it was.
When receiving criticism, chances are that a writer feels one of the two above statements. Sometimes both in rapid succession. It doesn't seem to matter whether the criticism is from a random stranger online, a friend or a paid editor. It doesn't seem to matter how often the author tells him or herself that criticism is an important learning tool and shouldn't be taken personally. There's always an initial emotional sting.
But receiving criticism is a necessary part of becoming a published author. Even self-published authors who eschew editing leave themselves open to reviews by the public. Those who wish to improve their writing skills have to accept criticism, which means leaving emotional reactions behind and learning to apply that criticism to improvement.
So the first step for the author is always to ask his or herself: Is this true?
Is there a grain of truth behind the criticism? When dealing with a professional editor, whether one assigned by a publishing house or one hired by the author, this is an easy question. The problem identified is real and needs to be dealt with. When dealing with other sources of criticism, it can be harder to figure out. A critique partner, an ARC reader or a independent review may not like your book and it's important to take the time to figure out the reason behind that dislike.
For example, I had one reviewer complain that they didn't like all the strange powers in my stories. Since I write paranormal romance and urban fantasy, there was little I could do about that particular criticism. But when my critique partner told me that an early version of my manuscript was unrealistic, I took the time to realize that I hadn't been consistent with how I applied my character's supernatural abilities. The first critique was a complaint about the type of book I write, while the second was something I needed to improve.
The next step is: What do I do about the problem?
Just because you've accepted there's a problem doesn't mean that you agree with the proposed fix for that problem. There's not much of a solution to be gleaned from "Your book sucks" but most helpfully-intended criticism includes suggestions for how to improve. An editor or critique partner may suggest different wording, or a different approach to a scene or character. It's up the author to decided whether or not that solution works.
This is where the delicate balance between accepting other people's input and protecting your own voice as an author comes in. I've always loved creative wordplay and often make up my own words or use unusual terms for description. In my first book, I used the word "eeling" to describe a character moving quickly through a narrow space. My editor flagged it as being used too often in the manuscript. I checked and discovered I'd used it twice, once for my heroine and once for a character who only appeared in a single scene. But I realized the editor was right. The word was distinctive enough to stand out, even if only used twice. So I kept it for my heroine and changed it in the other scene.
Last but not least is the trickiest step. Is it a standard or an opinion?
Editors often use a particular style manual to ensure consistent punctuation, grammar and formatting. Mine uses the Chicago Manual of Style. But the problem is that English is a constantly evolving language and the rules are always in flux.
For example, when including a texting conversation in my book, I initially put the texts in italics. My editor said that they should be in quotations, like any conversation. Per the style manual, my editor is right. But it didn't look right to me. But I didn't automatically assume that I was correct. I checked with other authors and did research to see which formats are commonly used.
In deciding to go against the style manual, I'm going out on a limb. There will be people who look at the book and will think that I've done something wrong. But I'm willing to take that risk because I think the standards are evolving and italics will become the acceptable standard in the future.
Accepting edits is a delicate balance between correcting one's blind spots and keeping one's voice intact. An author should put a great deal of personality into a book, but sometimes that personality affects clarity and understanding. Effective criticism, no matter the source, helps an author to find that balance.