> It was a Eureka moment, and entirely based on such a simple statement that was never brought up in lectures
Young me picked up the basics of cryptography at seven or eight, a couple of years before classes in the first foreign language began at age nine or ten. In Finland, for the Swedish-speaking minority, the first foreign language to learn is Finnish — often mentioned as one of the world's most difficult languages to learn. Neither the textbook nor the teacher mentioned how languages work, and specifically not how they are in no way related to cryptography. Young genius me concluded that surely the teacher will soon tell us how this crypto works, so we could move on. While waiting for that to happen, I skipped more or less everything. It took a couple of months to realize the actual situation, by that time the damage had been done. Picked up Finnish seven years later, the natural way through a colleague at a summer job.
That little omission had a detrimental effect on my average grades throughout the school years though, and therefore I certainly do not judge anyone's abilities based on their paper qualifications.