My early training was a disciplined Thumb(1) Thumb(3)Middle(6)Thumb(1)Index(5)Thumb(3)Middle(6) repeated over and over and over. You can memorize the tune this makes in an open Am or full C with added bassG. Then just play it til your ears drop off and your thumb can do it in your sleep.

Since then (forty years ago) I have built out and added variations and different strokes and runs until I can no longer recognize the original pattern -- but it s what made it all possible. And as said above, it has ervolved into my own style, which I guess someone might learn to recognize if they wanted to take the time. :>) Or they could jes' sit around and eat carrots or pick their nose.

A