When I started teaching my mantra was:
"I will teach people the right way from the beginning. The right technique, the correct practicing routine and all that. Then they will not need to relearn stuff when they are older, because their foundations are perfect."
This is the error of foundationalism applied to teaching. The general claim is: "teach students a set of basic secure foundations and that will prevent errors in the future".
The problem is that no such foundations can be found, even if they could exist. One way to see the problem is how it leads to an infinite regress. Any claim to be a basic truth must be justified by other truths, which must be justified by others still. What looked stable at first was actually built on turtles all the way down. Karl Popper gives us the alternative with his theory of rationality.
Knowledge consists of ideas in the form of guesses. The guesses are always some kind of purported solution to a problem. Those ideas are subject to selection pressure in the form of criticism, and through that process the ideas that survive become adapted to solve the problem at hand. Knowledge is like an old house we are always repairing. The doorknob breaks, we fix it. The tap runs dry, we lay new pipes. Nothing is ever complete and we improve it bit by bit in a process where we address specific problems.
Instead of abstract prescriptions — "everyone must first learn proper finger technique" — start where the student actually is. "I can't play this scale" is a perfect problem. It tells you exactly what to do next. On and on it goes like that, never finished but always moving from one problem to the next.
As Burton Kaplan puts it 'Perfect is irrelevant. Better is perfect'