This is super-fascinating:
You want to learn the systems, or the analogies, of the relationships between things in a certain field, and how they interact with each other. Then ultimately you gain that knowledge so that you can shift your own thinking, so when you see a new problem you’re better able to solve it.
And if you spend time "highlighting" things in books... try again.
The basic thing is, we forget, and we forget at a very regular rate. People underestimate how much they forget, and people who are able to revisit their learning at a regular rate end up learning a lot more.
Is this a "listicle"? Yes, yes it is. But, it's actually not that bad. Learn from the folks of Netflix, GitLab, Facebook, Buffer, Basecamp, Etsy, and more.