I have been reviewing calculus seriously again these days, after years leaving it, since I want to improve the mathematics articles in Indonesian Wikipedia. Not only reading books and articles quickly, I also took up pen and paper and tried to prove some theorems and worked out problems.
I understand now why some people found it hard. I know some friends that barely passed it, and one of them tried n-th times before barely passed it (if I am not mistaken, n=4) and teased endlessly because of it.
Another friend of mine said mathematics is actually not that difficult, but it is tricky. It demands a fairly imaginative mind to go through the theorems and the problems quickly. My lecturer once described there were two approaches to solving problems in maths: the “corporal ways” and the “general ways”. The “corporal way” seem easy and obvious, but generally long and tedious (and perhaps needs lots and lots of papers). The “general way” require tricks and imagination, but are usually short and elegant. Here I will not ponder the obsession of mathematicians for “elegant proofs”.
I actually passed freshman level calculus with more than satisfactory grades, and could not comprehend what was the fuss of it being “difficult”. Clearly I was imaginative enough or (more likely) I spent enough time for studying it.
But now I find it actually difficult. Either I do not have enough time nowadays for learning maths, or (more alarmingly) my intellects and imaginative powers have eroded. The latter explanation is rather scary for me to think about