The closest I've come to this is when I was doing my (now on-hold, potentially permanently) MBA. Some courses (especially strategy, leadership, ethics, and law) were extremely good, but others (econ, accounting) were stuck on rote memorization and calculations.

It was the combination of a semester of econ+accounting, plus applying the knowledge of the opportunity cost concept that I had been exposed to in a previous class, that convinced me continuing in the program was not the most optimal investment for me (so here I am, slacking off on HN instead...).