In schoolbooks, expository text is supposed to objectively describe how things work, in order to equip readers with scientific knowledge and methods to understand things scientifically. But in fact expository text contains something richer. Any exposition is based on the expositor's own perspective. What's more, the world we exposit is not a natural existence, exposition itself creates the world to a large extent, and thus all objective expositions are based on subjective construction, the world itself is essentially a symbolic one. No one can teach expository text well without understanding this point, otherwise students would be left to exposit the world objectively, ignoring themselves, or theory and thought, and believing that the world is a natural reality beyond human's will. This could eventually make people enmeshed in the web of their own overcautious spinning.