A class on

Logic. I was never good at math and had little interest in computers (There was no JavaRanch in 1990 to help us noobs!). I was taking a lot of electives in anthropology and

philosophy, so I signed up for a course in Logic thinking it would be about

Rhetoric. That's where it started, but it quickly moved on to

Mathematical logic like Boolean logic and formal proofs. For some reason, probably because it wasn't presented as boring old numerical "math", everything clicked into place and it opened up a whole new path for me. I finished my Bachelor's degree in Literature and wound up getting a second Bachelor's degree in Computer Science thanks to that class.