The Doubt of Manas

Consciousness can contemplate relatively abstract concepts, whereas the manas, because it clings to numerous dharmas, possesses inferior discriminative wisdom. It struggles to correspond with abstract thinking and invariably seeks firsthand experience; only what it sees with its own eyes does it deem real and accept. Therefore, if the manas harbors doubt about a certain matter, it persistently clings to it, constantly dwelling on the issue until it undergoes the experience itself, only then relinquishing the doubt within.

The saying "not stopping until one reaches the Yellow River" refers precisely to the manas. If the manas fails to reach the ultimate source of a matter, it refuses to give up. As long as doubt about something remains, it tenaciously holds on, always seeking to investigate until it understands. It persists until there is no path left to tread, continuing until it runs into a southern wall before finally turning back.