Spaced repetition
https://en.wikipedia.org/wiki/Spaced_repetition
How to Learn a Language: INPUT (Why most methods don't work)
https://www.youtube.com/watch?v=J_EQDtpYSNM
Stephen Krashen on Language Acquisition
https://www.youtube.com/watch?v=NiTsduRreug
Input hypothesis
https://en.m.wikipedia.org/wiki/Input_hypothesis
Comprehensible output - Wikipedia
https://en.m.wikipedia.org/wiki/Comprehensible_output
Mind hack: 7 secrets to learn any new language | Steve Kaufmann | Big Think
https://www.youtube.com/watch?v=Evbwtef8_-g