[dredmorbius]

It's also ... if not absolutely necessary, then tremendously helpful to the process ... to observe the subjects' expressed understanding and see if that matches the lesson or message you're trying to convey.

This distinction to me is what distinguishes various informational approaches, in which delivery is one-way, from instructional approaches, in which the teacher closely observes and monitors students to see what understanding they're forming, and to bring them back on course if they're straying from it.

This is challenging at scale, or at distance, or over time (e.g., in writing a book that's used passively in instruction). It's a chief reason I suspect that various methods of scaling instruction perform poorly. It's why even generative-AI approaches to machine-guided instruction are likely to perform poorly --- such tools can explain material or respond to prompts, but it seems don't of themselves address the monitoring-and-guidance approach.

That said, in technical contexts whether in school-based teaching, professional training, or marketing support / vendor-based instruction, efficacy can be hugely improved by adding this step.