This reminded me of the wonderful book, Zen and the Art of Motorcycle Maintenance by Robert Pirsig. It revolves around the Socratic question: “And what is good, Phaedrus, and what is not good – need we ask anyone to tell us these things?”
In the case of Giovanna Morganti (mentioned below), she follows the age-old tenets (decant only when necessary, keep the cellar clean, start with beautiful grapes, and taste often). In painting, there are tried-and-true techniques to practice as well. But who knows where our muse will take us? We have to follow, if we want to make our own paintings and not someone else's.
Maybe your painting is good because your eye is like no other in discerning the mood of a scene. Maybe your brush can describe a lively energy, a graceful passage, a poignant combination of colors, a rich soulfullness or eloquent simplicity. Or, maybe the painting was fun to do or captured a memory for you, or was given away to someone, or taught you something about yourself or the world.
Politely tell the critic (inner or otherwise) that "I appreciate your concern, but I'm not doing it for you. I'm doing it for the...(fill in the blank. For the practice, for the fun of it, for the blue herons, for the stars.)".
When I was starting out in college, getting serious about art, I read an interview with Bob Dylan where he said he didn’t have time to read what people wrote about him. At the time, I thought it strange, because I was involved in the left-brain study of ideas, opinions, philosophies, styles & techniques. Why wouldn't you participate in that? But it’s true that the muses live in a completely different universe from the critics.