Earlier quoted context omitted.
Subject categories such as "math" are also very broad. I struggled with math in elementary school, because it was mostly about memorization. 3 + 5 = 8. 6 x 7 = 42. Learning and being able to spit out those facts as quickly and flawlessly as possible was most of what I remember about math as a young kid. I was never good at that. I still am not good at that. I got Cs and sometimes lower grades in math. Somehow, though…
You struggled with math in elementary school because of deeply flawed teaching. Even at that early age, it's not hard to understand that "3 + 5 = 8" is not something that you'd need to literally memorize. Of course, the fact that teaching quality can vary to such an extent is itself noteworthy.
For what it's worth, I struggled with math in elementary school and especially high school -- I failed algebra I, then passed it with a D; then I failed algebra II before passing it* with a D. It wasn't until I was forced to take a business calculus class in my 20s that it started clicking, and I assure you the quality of instruction wasn't any better at the college level than it was in high school. (I did eventually graduate with honors with a math degree.)