Just went with my MFA classmates to see a production of Seminar at the Roundhouse Theater in DC. This is a play that's about four aspiring writers who are in a workshop with a crusty old instructor who alternates merciless abuse with tepid praise. It was extremely enjoyable. However, most of it was not specific to writing. It could've been about any creative profession. You could have replaced "writing" with "coding" at any point and made the whole thing about computer programmers and it still would've worked (well, except for how computer programmers don't really struggle economically).
One thing, though, was specific to the writing profession and rang fairly true. The very first week of the seminar, the professor critiques a woman's story for being incredibly dull and lifeless. And after he leaves, she rails about how she's spent six years working on that story and about how all these other well-known professors (she mentioned Frank Conroy and Tobias Wolff) had really loved it.
That's something that definitely happens, and I think it's very particular to the way that people begin writing. When people begin writing, they often only write for class. They might really like to write and really like the feeling that being a writer gives them, but they haven't yet processed that writing is something you should do all the time and do on your own. They need the motivation of class to produce anything. And, for many people who sort of thought about beginning writing careers, their first writing classes were in college. And then when they leave college, they stop writing, because there's no more class.
Many writers go through a several year long fallow period before they start to realize that they're going to need to write for themselves now (I think this also happens to writers who leave their MFA programs). And during this time, they'll reread, revise, and polish their best undergrad pieces: the ones that brought praise to them from their professors and that made them feel like they could be writers in the first place.
These pieces, though, are, almost invariably, not very good. What people don't understand is that when a professor says something is "good," what they really mean is "better than I expected." And sometimes (oftentimes) professors' expectations are very low. It's certainly a good thing to write one of the best stories in an undergrad workshop (better than writing one of the worst ones), but even the best story in an undergrad workshop usually doesn't come close to actually being a good story.
Part of the process of becoming a writer is learning to replace the professor's judgment with your own. Because, in most cases, professors aren't going to be nearly hard on you as they ought to be. In most cases (and for most people), it would be counterproductive for a professor to be as hard on you as they ought to be. You will accept criticism from yourself that you would never accept from another person. I can dismiss an entire novel as garbage. But if another person told me it was garbage, that'd be devastating (and I probably wouldn't listen).
I've never really heard another writer talk about this (in fact, I've heard the opposite. I've heard many writers talk about how they don't know when their work is good and when it's bad), but I think it's very important to have your own independent sense of your work's value. I don't understand how people can write something if they're not, on some level (even if it's only in a relative sense like 'this part is better than that part' or 'this story is better than that story') able to evaluate it.
Anyway, part of the process of acquiring your own sense of judgment is learning to let go of stories that your professors told you were good. There's something very comforting about that seal of approval. It feels like a promise. But it's not. A professor's judgments are meant to guide you; they're not meant to override your values.