During in-class discussions, students often but inadvertently make the same mistakes over and over again… say, thinking that or . Naturally, such mistakes need to be corrected, but hopefully politely and in a memorable way.
After the third or fourth such repetition of the same mistake during a semester, I’ll try to lighten the mood by saying, “You think that you can do these things, but you just can’t, Nemo!”
Pop culture reference:
See also my one-liner about the Third Classic Blunder: https://meangreenmath.com/2013/06/07/laws-of-logarithms/