What is the KEY limit on elaboration and self-explanation?

The explanation must be generated by YOU — reading someone else's is far weaker — and you need enough prior knowledge to generate a CORRECT explanation, or you reinforce misconceptions.

The power is in the generation. Studying a worked, expert explanation is passive and produces much smaller gains than struggling to produce your own; the effort is the mechanism. But there's a trap: if you lack the background to explain correctly, you may confidently generate a wrong explanation and cement a misconception. So self-explanation shines once you have a foothold in a topic and can reason toward the right answer — it's a tool for deepening and connecting, not for conjuring understanding from nothing.