Stuff you learned and forgot feels like rent paid. You lived in it for a while but are now left with no equity in it. Most schooling only rents you some knowledge for a while.
You’re left with only enough knowledge capital to find and rent it again. Like knowing the address of apartments you’ve rented before. I don’t know much but I’ve rented a lot of stuff over the years. My address book is nearly full.
Spaced repetition learning methods can fix this to some extent, but it means making a conscious decision when you learn something: do I want to know this for a while or forever?
I think it's possible to create an approach here which doesn't really require discrete decision-making. New material is optimistically added; when reviewing, you "pass" on stuff that's uninteresting; that operation acts like a soft-delete, resurfacing the content much later, etc