By humbling I don't mean in a negative way; rather in a way that made you really appreciate the subject by giving you a new mental model by rewiring your brain.<p>For me:<p>Programming Languages A, B and C by Prof Dan Grossman on Coursera.<p>It taught me the inter relations between different programming paradigms and how to pick up new programming languages. More clearly what to look for in the documentation to form a working mental model of a new programming language.
I'm not sure if "humbled" is the right word or not, but Calculus II had a somewhat profound effect on me. I think it was studying Calc II that I first started to feel like I could finally start to see at the least the shadows of the inherent appeal of math. I also felt like Calc II was a big step towards understanding the level of math that starts to have real world applications outside of contrived / toy examples that you find in textbooks.