首楞嚴義疏注經 10.322

10.322

示虛妄也。真猶實也，行陰若非汝體，何得相代不停？又若實是汝身，何不知覺生滅？非汝不可，是汝無憑，故知虛妄。則汝下結想名，密移難覺，故云幽隱。

This shows its illusory nature. "True" is like "real": if the aggregate of formations were not your substance, how could it continuously substitute without ceasing? Furthermore, if it were truly your body, why would you not be aware of its arising and ceasing? That it is not you is untenable; yet that it is you has no basis—hence we know it is illusory. From "Thus, your" onward concludes with the name of the thought: secretly shifting and difficult to perceive, hence it is called "obscure and hidden."