Criticism is one of the hardest things in the world to accept!
I know that I get pretty prickly when I hear my girlfriend tell me that my desk is messy or my work is sub-par, and that's the stuff that I'm not very protective about. Now imagine how much harder it is to hear that the book or story you spent months working on doesn't even rate a 3- or 4-star review by some random reader. Then they go on to point out all of the flaws and mistakes--each one like a dagger to your heart.
But over time, I've come to accept and even value criticism. And not just from experts (editors, highly valued colleagues, etc.), but even from people who have no idea what they are thinking or saying.
For example, as I started writing The Last Bucelarii (Book 1): Blade of the Destroyer, I was telling my girlfriend about how I was having difficulty adding emotional depth to my character. In the course of the conversation, she said this to me:
"If you want to add depth to the character, you have to have that depth first. You can't develop depth from behind a desk."
Bam! Took my legs right out from under me. It felt like a criticism, that I was so focused on my passion of writing that I wasn't living.
But then I thought about it, and I found out how to use that. Instead of trying to generate some emotional depth for a character, I began to use the things in my own life that make me a deep person. All of a sudden, something that seemed like a criticism became the answer to my problems.
Another great example: one of the reviews for my first novel--In the Days: A Tale of the Forgotten Continent--talked about how my characters lacked depth and showed very little emotional growth. A hard thing to hear, but I have taken that to heart. Now, it is a huge part of the stories that I am writing, and I believe that they have gotten better as a result.
So, as hard as criticism is to hear, boy is it helpful! If we could all be just a little less prickly, we could become so much better in so many ways. The criticism given to us by others will help us to make improvements in areas we may not even realize are weaknesses, thereby making up better for it in the long run!