I think it's somehow a curse of creative people that we tend to be a bit insecure. Maybe it's part of the creative nature; maybe it's due to the fact that we submit ourselves to constant criticism in the name of improving our craft.
We've probably all experienced those moments when you look at something you've written and thought, "This sucks. I suck. My writing will never go anywhere." While I do think it's important to be aware of our weaknesses so we can improve, that kind of thinking never did anyone any good.
We can believe in our ability to improve.
We can believe in our strength to deal with criticism and apply it to our work.
We can believe that, even with mistakes, the fact that we have written anything at all is a triumph.
We can believe that our hard work will pay off-- and is paying off even now.
We can believe in the validations of our work, in addition to the criticisms.
We can believe that our accomplishments, no matter how small, are worthwhile.
So, my friends, have confidence in yourselves as writers. Allow yourself to look back on all the good things you've done and find value in them. We're all works-in-progress, but that doesn't mean we can't acknowledge all we've achieved so far. Go forth and believe in your ability to be amazing.