Too much polishing and you spoil things. There's a limit to the expressibility of ideas. You have a new thought, an interesting one. Then, as you try to perfect it, it ceases to be new and interesting, and loses the freshness with which it first occurred to you. You're spoiling it.
How can we say nobody's perfect if there is no perfect to compare to? Perfection implies that there really is a right and wrong way to be. And what type of perfection is the best type? Moral perfection? Aesthetic? Physiological? Mental?