My advisor for my math degree told me straight-up "You don't really understand a math course until you take the next class in the series." I'm really glad he told me that, because it sharpened my perception of how well I understood different subjects. It also shaped which classes I took for the rest of college, tending towards depth over breadth.

Too many students think that math is just an arbitrary collection of arbitrary steps. It all makes sense, but you have to have at least one teacher contextualize it for you in order for all of it to click.