Being a teacher myself now, I tell my students that, when revising, they need readers (at least one), who will tell them the truth about their writing and provide feedback. I think this is true no matter how long a person has been toiling away the business. Writers need second opinions. And these second opinions must be somewhat objective (sorry, Mom). Without some feedback, we are privy to assume that the readers of our final drafts think the way we do, and this can lead to logic errors, especially when writing fiction.
Now, I've made it a sort of resolution to try to get feedback from at least one person, preferably a writer whose work I admire, before submitting anything. Even if I don't agree with another's critique it's important to consider all feedback before dismissing it. This is how a writer can continue to grow, even after the terminal MFA.