Every professional writer I've ever talked to, from New York Times Bestsellers to first time self-published, goes through the same emotional process about their work, running along the spectrum from "It's brilliant" to "It's crap" and back again.
Personally, I go through a kind of separation anxiety. While I'm working on a manuscript, I have a decent awareness of the level of quality (backed up by my beta readers). But after I walk away, all the flaws become magnified in my mind. I start obsessing, convinced that my writing is nothing but the flaws, that they overwhelm any other redeeming features.
The longer I go without looking at a particular work, the worse I convince myself that it is and the harder it becomes to make myself go back to it.
This becomes a particular challenge since I find I also need at least two or three weeks of separation in order to approach the manuscript with fresh eyes. When I finally pull it open, I'm mentally cringing but as I force myself to peek through my fingers, I discover that it isn't as bad as I thought. I've done more work than I remember, I've set up and resolved my subplots properly (and if I haven't, it's usually a quick fix).
The more I go through it, the more relief I feel. I start to feel proud of what I've done again. I start to have faith in my skill and my work again.
What I've learned is that I need to remind myself that those feelings of anxiety and unworthiness are as false as any message that comes from depression. While I don't wish to overstate my abilities, I shouldn't underestimate them either.
Maybe this is part of the "Impostor Syndrome" that Dr. Young spoke about at RWA. It's too easy to dismiss skill as luck or chance. False modesty becomes underestimation which becomes a sense that one has falsely represented his or herself. After all, if it's only luck, then there isn't anything to fall back on when luck fails. As it inevitably will.
But the thing is, no one becomes successful only by luck. It plays a part in providing opportunities, but without the talent and drive to take advantage of those opportunities, there cannot be any achievement.
Easy to say, not so easy to believe, not deep in the gut where our secret fears hide.