I think it's meant to apply to a single, atomic concept that the audience is suitably prepared to understand. It couldn't be something like "how to build a car

I think it's meant to apply to a single, atomic concept that the audience is suitably prepared to understand. It couldn't be something like "how to build a car starting from a lump of steel" -- that would not be a single, atomic idea. "How anti-lock brakes work" might be a better idea to explain in simple terms.