The mathematical pedagogy to which you refer is aimed at teaching a broad canvas of essentials. This is good if someone has decided what those are on your behalf.
Sometimes, though, if you need to just learn something, say to understand a paper or a particular result, you need to find out what you need to learn, and this is perhaps a case in point.
To learn basic graduate level algebraic and analytic number theory would be a few years, from scratch. And then you find out that you spent too long on cubic reciprocity when you needed to learn more about L functions and modular forms..
It is well known that a vector space always admits an algebraic (Hamel) basis. This is a theorem that follows from Zorn's lemma based on the Axiom of Choice (AC).
Now consider any specific instance of vector space. Since the AC axiom may or may not be included in the underlying set theory, might there be examples of vector spaces in which an Hamel basis actually doesn't exist ?