It happened to me during second semester Calculus. In first semester, the professor found out that I didn't do the assigned homework (worth no points) and said that I would "die" in next semester. Sure enough, it happened. What I learned over the years since that time is that some things just take practice or effort. The difference in Calc 2 was that the problems became non-intuitive and virtually everyone is forced to learn some identity or transformation to solve a problem (usually involving trig functions). Basically second-order formula plug and chug, but "effort" required to be able to do it right with time constraint.

I still didn't espouse the value of hard work until I've gotten out of college. I tried to cruise by like I always did, though it increasingly became untenable. What made me really understand working hard was actually through sports. There, I had no illusion of being superior, and it's established that you get better through practice. You get to see yourself getting better each time, and put yourself to the test. True iteration.