The Doubt of the Manas

The mind consciousness can think about rather abstract things, whereas the manas, because the dharmas it grasps at are extremely numerous, has a coarser faculty of discernment and does not easily resonate with abstract thinking. He always wants to experience things personally, believing something to be real only when He has seen it with His own eyes, and only then can He accept it. Therefore, if the manas still has doubt about something, He will keep dwelling on it in His mind, with every thought fixed on that matter, and only after experiencing it will He let go of the doubt in His mind.

The saying "one does not give up until reaching the Yellow River" refers precisely to the manas. If the manas does not reach the ultimate bottom source of a matter, He will not give up; if He still has doubt about something, He will keep holding on to it tightly, always wanting to investigate it thoroughly, until there is no path left to take—only after hitting the southern wall is He willing to turn back.