Complex ideas may be hard to learn in part because their components overflow working memory. Given that Spaced repetition memory systems make memory a choice, memory augmentation may be one interesting solution.
Matuschak, A., & Nielsen, M. (2019). How can we develop transformative tools for thought? Retrieved December 2, 2019, from https://numinous.productions/ttft
What makes these subjects difficult? In fact, individually many of the underlying ideas are not too complicated for people with a technical background. But the ideas come in an overwhelming number, a tsunami of unfamiliar concepts and notation. People must learn in rapid succession of qubits, the bra-ket notation, Hadamard gates, controlled-not gates, and many, many other abstract, unfamiliar notions. They’re imbibing an entire new language. Even if they can follow at first, understanding later ideas requires fluency with all the earlier ideas. It’s overwhelming and eventually disheartening.