For me, it’s about internalizing the reasoning. If I always know the answer to the question “why,” I can reinvent and apply the relevant math. Most mathematical methods were created for a clear purpose and their formulas, definitions, and processes reflect that purpose. I try to identify the key jump in reasoning you need to derive any of them and I usually remember that because it’s cool, or I was proud of myself for figuring it out, and whatnot.
Before college, math tends to be very “solve this because” without many proofs or applications, so while you might enjoy it, it’s hard to keep track of the minor details along the way- the reasons why formulas are that way or theorems that highlight quirks of the system. You might remember the math you memorize, but you won’t be able to use it to build intuition of harder concepts because you never internalized the reasoning.
That’s one of the reasons why I enjoyed going back and learning algebra II- level material after I completed my degree- there were so many cool and useful things that I didn’t know about, understand, or even try to remember
That's exactly why I hated maths for the past few years. It was all about memorization. I loved maths in the primary school, not because it was easy but because everything made sense. I did x y equations in the fourth grade in the form of little animals. It made a lot of sense. It took me years to really understand what x & y mean. I understood the animal version immediately but X & Y confused me for so many years.