I personally found that in general it is quite hard to figure out which math you need to fully understand a certain result if you don't already know the math. If you start with an overly ambitious goal (for example if you start with the Einstein equations of General Relativity and say to yourself: 'Lets backtrack to see which math I need') I suspect that you will have trouble figuring out which math to learn

Noted, but I do have the advantage of being able to ask. The next post will ask, "for each topic, formula, or problem on this list, what math do I need to know to understand and solve it?"