If you’re in the habit of asking yourself whether what you’ve just finished writing is any good, don’t.  The answer is always no.  Ask that question, and you give everyone who ever tried to put you down another chance.  A piece of writing needs to be rigorously and objectively edited for spelling, grammar, tightness, and clarity, sure.  But get subjective, get personal, and you’re indulging in self-sabotage.