There's a few, all happening in College, because that's when I started taking art seriously, and I think the worst offender was either my animation teachers (plural! I had two who did this) who refuse to critique my sketchbook because "You're an illustrator so it's different and I don't want to come off condescending" and like...well I guess you at least acknowledge your insane superiority complex to other art degrees. Wild since you both started off as illustrators and most illustrators take animation courses. Wild.
And then the other was a teacher who I think was going through a real rough time and said "If you don't make it in 2 years then what even are you doing? You'll never succeed after that so either delete your social media and change your art name so no one will know who you were or just go into accounting." Which is maybe the worst advice I've ever recieved. And I even knew it at the time that it was bad advice, but he's a white guy who came from a position where he graduated in the 90's when it was a lot easier to get entry level illustration jobs, he had an agent out of college, so he was living off of pure illustration in 6 months. Yes he worked hard but hot DAMN good thing he didn't fail or he would have just thrown in the towel. He would have never known how good he truly was if he only gave pursuing art 2 years.
And like what even success, right? Like we all work other jobs when we have other jobs. It's fine. The push to become a full time illustrator is honestly overrated.
Funily enough the same teacher who told us that later went full Papa bear when a visiting artist told us we were terrible (we were 1 month illustration students at the time so we were terrible), and like totally was like "Don't listen to that guy! he's an asshole! You don't want to be like him! Go have a real life unlike that guy, that slimeball, that dickweed! he has no friends!" so like...he wasn't terrible all the time just occasionally he had some doubt that I think was more centered on himself than us.