If you want to suffer near-constant frustration as a writer, just do one thing: identify with your writing.
Think of your writing as a measure of yourself, as a measure of your significance and your capabilities. When your writing sucks--which it inevitably will from time to time--you suck. Q.E.D.
It's all too easy to fall into this trap, isn't it?
Yes, your writing comes from you, but it is not you. And most importantly, it is not a measure of your value as a person.