I did a fairly rigorous linear algebra course in school, and it went over my head despite passing it.

Saw it explained in a single slide of Andrew Ng's ML course and everything clicked perfectly.

Where I lived math was taught like fucking shit, it was all algebra and zero context as to why it could be useful in real-life scenarios, zero abstraction such as visualization or metaphor. Everyone involved in concocting that pedagogic aberration should feel terrible about it.