Why this thing exists, and what the evidence actually says about building speed.
One note, one string, two beats. Then everything else gets added one variable at a time. This is the exact routine, start to finish.
A book about talent hotbeds, five YouTube guitarists saying variations of the same thing, and a plateau that would not move. This is what came out of it.
Perfect reps wrap myelin around the circuit and myelin is the mechanism of skill. It is a great story. The evidence for it is much thinner than the guitar internet suggests.
Comfort, edge of ability, speed burst. Most players spend their whole practice session in the wrong one and wonder why nothing moves.