It's common for me to read something, and forgot it even existed. I can't look it up unless I know it exists. With flash cards, I am reminded that it exists every once in a while.

As an example, here's a simple card: What is the recommended way to traverse all the files (including subdirectories) in Python?

Answer: scandir and not os.walk

os.walk is my standard goto. Then I learned about scandir, but kept forgetting that there was a better alternative to os.walk. So I made a card for it.

The other answer, of course, is speed. If I'm going to Google "what is the alternative to os.walk?" or something similar every time I need it, it adds a lot of friction and I simply won't bother. And no, I don't do this often enough that looking it up each time will force it to become ingrained.

And frankly, when you do math/physics, you do need a number of concepts in your head. Solving a complex problem requires multiple parts/stages, and solving requires you to have them in your head so you can put them together. My biggest mistake when I was in grad school was thinking I could get by without memorizing. It worked fine for undergrad level math, but it was a real problem when I took higher level courses. The professors were split on whether memorizing is a good idea, but the fact is the professors used this stuff a lot more than I did.