I’ll go first: “You have to have children when you’re young,” told to me when I was in my late 20s, with no desire to ever have kids, and no means to support them, by someone divorced multiple times with at least one adult child who does not speak to them.
Also: Responding to “How do I deal with this problem?” questions with “Oh, don’t worry about it, it’s enough that you’re even thinking about it!”
“Try again.” Particularly involving schoolwork. Derelict teachers then complained when the result of trying again would be identical, to the letter, for the same reasons as the first time. But teach? They did not.