Deliberate Practice
Most practice is just busywork. This is the kind that actually rewires you.
Grounded in the research on practice (learning method)
So it's just... practicing hard?
No. It's a specific thing. K. Anders Ericsson coined deliberate practice from his 1993 study of violinists at the Music Academy of West Berlin (with Krampe and Tesch-Romer). It's structured, full-concentration work designed to fix a specific weakness, with immediate feedback, repeated past the point of comfort. Not fun. Not casual reps. A targeted attack on the exact thing you're bad at.
I've played guitar for years though
Years of playing isn't years of improving. Ericsson calls your default mode naive practice: doing the thing and hoping. You hit autopilot, stop getting better, and plateau for a decade. Most people who've done something "for 20 years" are running year one on repeat. Time logged is not the variable. How you spend the reps is the entire game.