> from first principles

I don't think that phrase means what you are trying to say here.

What it doesn't mean: - learning by doing

I believe it generally means: a formalization that comes after a subject is understood so well that you can reduce it to "first principles" that imply the rest. Or, the production of a hypothesis by deduction from widely-accepted principles.

Honestly, I read that passage as Carol realizing as she spoke that she had been underwatering that spot semi-consciously the whole time. That’s one of the things about expertise gained by doing. We don’t always realize exactly what we’re doing well enough to communicate it until we reflect on it later.