Shu Ha Ri
Around 2000, I was writing about the 3 levels of listening, and someone introduced me to Shu-Ha-Ri. They have been a mainstay of my writing, teaching, speaking since then.
Here is an article explaining Shu Ha Ri, from the early 2000s: Shu Ha Ri (PDF)
Then, in 2015, I was looking for the radical simplification of agile, and I ran across Kokoro extends Shu-Ha-Ri with “Heart”