The mind consciousness's inference and deduction is not contemplative practice (vipaśyanā-caryā) or Chan investigation

When cultivating meditative concentration and contemplating the breath, the mind consciousness should only observe the movement of the breath—knowing the breath entering and leaving, knowing whether the breath is long or short—without adding an extra thought asking what the source of this knowing is. Whatever the final result of knowing may be, that is a matter for later; the result has not yet emerged, so do not speculate. The mind consciousness's reasoning is merely its wishful thinking, and wishful thinking can never solve a problem. Only when the mind consciousness and the manas are both willing can things click into place and be resolved perfectly; only then will the final result appear as it truly is—and that is what is called realization.

The mind consciousness's reasoning is not bad in itself, but it is merely a signpost. Whether to actually walk the path and how to walk it still depends on the manas's decision. If the manas does not decide, no matter how the mind consciousness points the way, it is useless. Sometimes, when the mind consciousness does not reason, problems can still be solved smoothly; reasoning actually delays matters. If the direction is correct, not reasoning may allow one to proceed faster and more steadily. Using the mind consciousness too much is not a good thing: the more the mind consciousness is used, the more incompetent the manas becomes; and when the manas is incompetent, it means you as a whole person are incompetent. If the operating and command system has problems, how can anything be operated at all?

Cultivation is the work of a fool. If one is too clever, one will not do things in a simple, honest manner. Let the mind consciousness point out the general direction, then close your eyes and rest, quietly supervising—that is enough; do not meddle too much. Once the manas, relying on its own ability, walks out and reaches the destination, its capability is incredibly powerful. If it has to be dragged along by the mind consciousness, the manas becomes feeble-minded and incompetent, and no great thing can be accomplished. 

The mind consciousness's reasoning is, in essence, delusive thinking. Delusive thinking means not having seen; once one has seen, it is no longer called delusive thinking. Some people use the mind consciousness to imagine an eighth consciousness performing some function in some place, and then define this as seeing one's true mind and attaining enlightenment—no need to eliminate afflictions, no need to cultivate meditative concentration; at most, a few minutes or a dozen minutes of the mind settling down will suffice. Everyone should be able to know what the consequences of doing this are. If this counts as enlightenment, then dreams count too: if you dream of mountains of gold and silver, you should wake up and strike it rich. But a dream is, after all, not reality, not fact. How can the speculations and various machinations of the solitary mental consciousness be taken seriously? If you want great wisdom, genuine wisdom, then honestly cultivate meditative concentration and contemplative practice (vipaśyanā-caryā) and investigate. Do not let the mind consciousness nimbly and flexibly deduce results; if the manas does not accept that result, everything the mind consciousness does is wasted effort.