This happens to me quite a bit. I'll be writing, revising, whatever. Then I'll look at other people's work, read agents blogs - everything I should be doing to improve myself in my craft.
Then, out of the blue, I'll get this intense fear that I'll never be good enough. That no matter how hard I write, how hard I try to get something right, no one but me will ever like my work.
I reason with myself. I tell myself that I have a career planned out, a career I look forward to, wish to do, plan to revel in. Medicine is going to be my passion, writing my life. I can't live without stories - they visit me throughout the day, play themselves out in my head when I'm trying to sleep. If I write them down, they leave me alone. But I have more than one goal in life. If I'm not published, I can be a good surgeon (That isn't the least bit subjective. You can either do it, or you can't.)
The only problem is that after you've written something down, you have this intense need to show someone else. And it's then that you realise you first draft might not be as good as you first thought.
So you revise. You re-write. You edit. You pass your work onto good beta's, and they help you make it better. You find the right beginning for your story, the right middle, the right end.
And then you worry that it won't be the right beginning for anyone else. That they'll put it down thinking - this character is just reacting with grief at the moment - this is YA, there should be something exciting on the front page. Never mind if that something exciting confuses, it should be there.
Now, I know people don't think like this (Well, some people do, but I don't really want to know them when it comes to this book. Others - maybe. But they're not going to be the right person for this one.)
I consul myself. I tell myself that even if it never is published, it will be the best that I could make it at that time. That I will have achieved something extraordinary in my life.
It doesn't work. So often the bruising of the ego is so bad that I have to talk myself back into writing again, and then only so I don't go mad with lack of sleep.
So how to fix this? You can't. I can't, anyway. Maybe if I had the validation of being published, it would help, but I doubt it. The practical part of my mind talks of trying as hard as I can, failing, and then moving on to the next project, which may do better. This is why I set deadlines for myself, so I won't keep trying.
There is only one thing that ever helps. Creating something new.
So that's all the advice I can offer. If someone doesn't like what you've written, move on, create something else. Practise.
But above all, write.
A fitting start to Nanowrimo, I think :)