Go ahead and down-vote me now, I'm going to criticize academia here. The question was "which courses have had the greatest impact on you?" and not "which courses have had the greatest POSITIVE impact on you?" I am sad to say my junior year honors literature course had the most impact on my career. One of the assignments was an analysis of one or two Matthew Arnold works (Matthew Arnold's a 19th century poet & critic…
As a high-school Valedictorian, I too was set up to do very well in academia, but could tell it would be too hostile and backwards from what I wanted. You're expected to be way too submissive and highly discouraged from original/independent/unpopular thought that conflicts with those already invested. I was excited to get to "real education" after conforming to high school but the rules only tighten, and it's 100x hyper-political.
So I skipped it, self-taught, and started stacking money. No use in casting pearls before swine and try to "fix the system" (and likely just be sacrificed to it, like Semmelweis). To the people trying to fix problems, thank you for choosing to be the martyrs so I don't have to; on the other hand, Max Planck had the right attitude when he said things advance via funerals, so why let it be your funeral?
Academics are good for bagging my groceries and delivering my pizza though, so I am grateful for their contributions. (I'm dunking on them here in jest, but PhDs -- pizza handling and delivery -- are above midwits but just often grossly misapply efforts. Sad to see).