I shall not watch that guy, talking funny and speaking too many words while expressing very little, but I can say this:
I had terrible teachers. I ceased to understand anything in maths when I was about 11 years old. I could always perform tolerably well, my calculations were usually correct and I could do anything, but I hated it and I didn't understand it.
As an adult person I took my math book from high-school to do some math excercises instead of a crossword. I didn't remember how to do them, I've no idea how to them, so I started wondering what the excercises want the solver to do, and how it works. After some time, I've checked my results, and to my surprise, I discovered that my calculations were correct, even though I didn't know how to them. I also noticed it was also a good fun.
Then I realised, that I was taught maths badly my whole life. All you need to do in maths is to understand what you're doing, and think logically (and know some conventions related to how do you write your calculations). But nobody has ever taught me maths that way. Always, I was only required to memmorise the procedure and execute it. That's why it was boring, that's why I hated it at school, and that's why my life is ruined.