Good question.
In some cases, you shouldn’t. If a quiet, honest place in you knows you’ve written something true and beautiful, don’t listen to anyone. Run to a studio, agent or publisher before someone makes you doubt yourself.
But listen to me over your mother, especially if she thinks you’re a fool, or a genius. Listen to me over the voices in your head, those yelling you’re a fool, or a genius. Sometimes brilliance takes a few drafts. Sometimes we grow so attached to hard-won words that removing one feels like amputation. In such moments, we need an outside voice.