I keep meaning to go through the entire "Learning How to Learn" course, but in the meantime, here are some reminders... https://www.youtube.com/watch?v=uG6pajrRAaE
Nautilus: How I Rewired My Brain to Become Fluent in Math, 2014-Oct-2 by Barbara Oakley
Understanding doesn’t build fluency; instead, fluency builds understanding. In fact, I believe that true understanding of a complex subject comes only from fluency.
In other words, in science and math education in particular, it’s easy to slip into teaching methods that emphasize understanding and that avoid the sometimes painful repetition and practice that underlie fluency. I learned Russian not just by understanding it—understanding, after all, is facile, and can easily slip away. I learned Russian by gaining fluency through practice, repetition, and rote learning—but rote learning that emphasized the ability to think flexibly and quickly. [Emphasis mine.]...
Fluency allows understanding to become embedded, emerging when needed.