I wanted to be an astronomer, and I knew that required lots of math. So I took all the math offered at my high school (up to limits and the derivative), even though my very good math teacher counseled me to go for a career in English or the humanities instead.

When I got to college I struggled with math. Although I had a great intuition for physical science, that will only take you so far. Without the math you really can't get any creative work done. But I stuck with it, and by the time I finished my astronomy degree
I was 3 undergraduate courses short of a degree in math, so I took them, passed with C's and got the second Bachelors. It damned near killed me, though. I'd never studied so hard.

My undergraduate grades were above average, but not superior. I was a B student. (This was before grade inflation!) The highest level math I was exposed to was partial differential equations and some complex analysis.

It wasn't until my second term in astronomy graduate school that I realized I was out of my depth. I hit a wall. I realized I might kill myself and eventually get a Master's in Astronomy, but I would never get any higher, never do any really creative work in research. I was destined to play Piano Bar at some community college, not Bach at Carnegie Hall. I quit and went to work overseas to get my head sorted out.

Math is like music, or foreign languages. Anyone can do it, if you work hard enough. But some people have a real talent for it, and they are the ones who get to do the really neat things. I envy them. They are very lucky people.

I've pretty much forgotten most of my calculus and DE, and my linear algebra and set theory--I haven't used them since I left school. I'm still pretty conversant with my trigonometry and algebra, because I use it in navigation a lot. So I have managed to retain pretty much what I had when I left high school.