Tim Gunn says, "Step outside of the monkey house!!"
How does this pertain to writing?
Well, sometimes, we as writers get a little TOO close to our work. So close, in fact, that we no longer smell the doo stinking up the place. I.e. the bad writing, the contrived plotlines, the cardboard characters walking around, the authorial intrusion permeating the entire thing. When this happens, we're not even aware of it. In fact, we're convinced that what we're writing is absolutely genius, and no matter what we do, we can do NO wrong.
This…this is when crit partners come in very handy. In short, you need someone to tell you… "Yo, this place smells like shiite."
It's very easy to get caught up in this. I've been there, and chances are, you have, too. It's not a sign that you're a bad writer. It's just a sign that perhaps we ALL need to take a few steps away from our work and get an aerial view. Look at the entire picture. Give ourselves some space and time away from our projects so that we're able to come back to it with our senses fresh and alert. You'd be surprised how something that seemed fine—great, even—will set your eyes a' waterin' the moment you step back to the project.
So, I guess my advice is this: Don't be afraid to step away from a project. Allow your senses to air out, and send it to people you can trust to tell you if you have indeed been living in a doo-infested stinkhole. The world and your book will thank you.