I dropped from an A to a B in a statistics class because I didn't know enough about traditional western playing cards.

The man was the laziest grader ever - he looked to see if you got the right answer, and if you didn't, half credit. He was also the kind of professor whose tests consisted of only 4-5 questions.

This question asked about the odds of drawing a "face card" from a deck. Without really thinking about it, I interpreted "face card" as "non-number card", i.e. jacks, queens, kings, and aces. I used the correct formula, did the math 100% correctly... but aces aren't face cards. So my answer was wrong because I used the number 16 when I should have used 12. Lost so many points I dropped from an A to a B. Tried to argue it, he didn't care.

The kicker? This was my third time taking college-level statistics. Not because I kept failing, but because the credits didn't transfer. Higher education is so broken that memorizing the homework problems by rote counts for more than actual knowledge of the material.