I once failed a subject during my masters (complex analytics and measure theory).
Next year I decided to give it everything I've got. I had grown to love it and could solve most problems they threw at me. Hand written an 80 pages long "book" distilled from all the notes, proofs and visualisations from all the lectures that year.

I only exerted this effort (even though I could've just "passed" this subject) because the lecturer was so damn enthusiastic about maths. Even though he wasn't a CS teacher this course was my best experience of a teacher at uni. He loved the beauty of the maths he was teaching and managed to make me love it too.

He was a maths geek and when I aced my final he told me he actually writes code too. He showed me some simulations he wrote while he worked on some theoretical nuclear physics stuff, because that's what he was into. Really cool guy. I wish more CS lecturers were as good teachers.