In 1989 I sat my first university maths exam and failed it. Badly. I was working full-time as an industrial chemist in oil refining and studying by correspondence — no classroom, no lecturer worth listening to, just me and the textbook. I was certain my bad memory had finally caught up with me.
I almost quit. Instead I rebuilt the way I studied from scratch. I stopped trying to memorise and started trying to understand — deeply enough that I could derive anything I had forgotten on the spot.
I finished the degree as the top mathematics student in Australia. Won two national awards. Got 100% on exams — not by remembering, but by understanding so deeply I couldn't get it wrong. That's what I teach. That's all I teach.