This may be exaggerated, but it’s true for me: I’m much more likely to agree with my critics (and adjust my writing in response!). Five people could praise a favorite line and then if one person thought it was silly, I’d probably start leaning toward believing it was silly. Some of this is good, adaptive behavior: you WANT readers who will tell you what’s wrong with your story and push you to make it better. But some of it is just Insecure Writer Syndrome™. For some of us, if one reader criticizes something we wrote, we suddenly can’t see the scene the same way and it will bug us until we fix it.
There’s such a thing as too much of this, but most of us have a healthy level of ability to take criticism seriously. We won’t throw our manuscripts in the fireplace and quit writing forever if someone dislikes our work, but we’ll obsess over criticism and it will seem magnified in our minds. This is generally a good thing unless it paralyzes our ability to draft without too much fear. However, much worse than this is its opposite: the authors who savor only the praise and automatically ignore criticism. These are the authors who are more likely to defend their work in the face of criticism instead of taking a good look at what they can improve, and these are the authors who think they have nothing to learn.
So they don’t.
Here's another blog entry of mine in which I offer a more sophisticated discussion of how to determine the value of criticism and how to apply it.