We know about formative feedback, metacognition, activating prior knowledge, and much else. Researchers mostly agree on the basics. There is still much to learn, of course, but it's fair to say that we know how to help people learn skills.
Like any area of expertise, learning about learning takes study. There is no reason to think that experts in, say, computer science, know much about how people learn computer science. Computer science experts have studied algorithms, programming, operating systems, networks, etc. Most have not studied human long-term memory, attention, schema abstraction, and so on.