I think Vygotsky's expression "zone of proximal development" means "one inferential step away", so in theory professional teachers should understand this. I prefer to imagine knowledge like a "tech tree" in a computer game.

When teaching one student, it is possible to detect their knowledge base and use their preferred vocabulary. I remember explaining some programming topics to a manager: source code is like a job specification; functions are employees; data are processed materials; exceptions are emergency plans.

Problem is, when teaching the whole class, everyone's knowledge base is very different. In theory it shouldn't be so, because they all supposedly learned the same things in recent years, but in reality there are huge differences -- so the teacher basicly has to choose a subset of class as target audience. Writing a textbook is even more difficult, when there is no interaction.