Lots of little light bulb moments, starting in college (80s).
When my calculus prof announced the list of students eligible to join the tutoring lab, my initial reaction was "who'd want to do something as geeky as that?" A few months later, when looking into the cost of renting vs dorm life, a paying tutoring gig suddenly sounded pretty good. Was also shocked to discover that renting for 12 months (with a roommate) was cheaper than R&B for essentially 8 months a year and being thrown out for breaks.
Since at that time fed loans were just enough to cover R&B, and I'd applied for and received a new work/grant position on campus, I realized how pointless it was to borrow when I could earn at least the equivalent here and there. No more student loans, cheaper better housing year round (let me work full time summers on campus in a related gig I got due to grant connections), no need for a car. I found it was pretty easy to get little side gigs all over campus: software work for Academic Development led to desktop publishing a writer's newsletter for my boss and to summer work testing incoming frosh, and school year math tutoring led to private tutoring (SAT for HS students, and college level), and a graveyard shift on dorm desk duty summer Saturdays.
I've naturally never considered not paying off a credit card every month (to avoid paying unnecessary interest), so I was shocked when I saw that a friend was only paying the minimum. My inner math tutor was calculating all that extra interest vs principal payment, while my friend just ignored it and paid the minimum to conserve cash. Ironically, he had the charge because of no cash at the time - brakes needed on his car. So my friend only used the CC as an EF, and paid the min to have cash for future emergencies. I tried to point out just how much he was paying in interest to have that cash in his pocket, essentially half the payment was interest! He listened, and paid it off (it was ridiculously small, like $60), but he didn't really go "OMG, that's crazy highway robbery", he just said "Oh, ok, if you say so. Whatever."