My current model of teaching and learning (self-teaching) is that to be effective, it needs to target a specific piece of information the student is immediately ready for. I want a word for such pieces of information, so let's call them useable bits. In a sentence, the teacher or learner's job is to present a stream of useable bits to the student with a minimum of non-useable bits. Most of the time, the vast majority of information the student receives is non-useable bits, and trying to sift the useable bits from that stream causes overwhelm and confusion.
Effective learning involves purifying information streams to contain a higher concentration of useable bits. There are multiple strategies for this:
Fast sifting: Learn how to more quickly and easily sift useable bits from a stream of non-useable bits. I think this is most students' default strategy, developed as a survival tactic in school where it's their only obvious option. It is unlikely to establish a new foundation, but instead establish a hodgepodge of trivia-like, quickly-forgotten extensions to the student's pre-existing foundational knowledge, resulting in precisely the kind of deeply inadequate learning outcomes we observe as a rule from the education system.
Building from a foundation: Structure the learning task so that the student's next useable bits that are also relevant to the student's priorities are always apparent -- we always know what the student is ready for next and we give just that information to them. This requires having a foundational grasp of the subject so that identifying the next useable bit that's also most relevant to the student's interest is obvious.
Digging a rabbit hole in which to lay a foundation: Focus on the first point of apparent uncertainty (the first non-useable bit), and recursively drill into it definitionally until that first non-useable bit becomes useable. This may be a deep rabbit hole. However, it hopefully results in establishing fundamental topic knowledge that will eventually allow a more focused approach to learning specific topics within the domain.