Imagination and conjecture are completely unreliable methods of practice.

Because sentient beings have limited wisdom and cannot contemplate deeply, and because their meditative concentration (samādhi) is insufficient, the deliberation (manana) of the manas also cannot function. For some of the deeper dharmas, they habitually resort to conjecture and speculation, and conjecture and speculation are merely the functions of the mind consciousness, bearing not the slightest trace of the wisdom of the manas. 

The most serious form of conjecture and speculation is to talk offhandedly, claiming that after enlightenment one can observe how the eighth consciousness gives rise to the faculties, the body, and the material world. "Faculties" (gen) means the bodily faculties, the physical body. As for how the eighth consciousness uses seeds to give rise to the bodily faculties bit by bit, and how it gives rise to the eye faculty, ear faculty, nose faculty, and tongue faculty, after enlightenment one might need to cultivate for another incalculable kalpa before perhaps observing a little, and about two incalculable kalpas would be needed to observe a considerable amount. "Material world" (qi) refers to the universe, the material world (器世间), the spatial environment in which sentient beings live. As for how the eighth consciousness uses seeds to give rise to the universe and the material world, even after enlightenment and cultivating for another incalculable kalpa, one might still not be able to observe it; about two incalculable kalpas would be needed to observe some of it. "Elements" (jie) refers to the eighteen elements (dhātus): the six faculties, six sense objects, and six consciousnesses. As for how the eighth consciousness uses seeds to give rise to the six faculties and six sense objects, even after enlightenment and cultivating for another incalculable kalpa, it would still be very difficult to observe; about two incalculable kalpas would be needed to observe some of it. As for how the eighth consciousness uses seeds of consciousness to give rise to the six consciousnesses, after enlightenment and cultivating for another incalculable kalpa, one could observe some of it, but not observe it completely and fully. 

But no matter what one can observe, if one's own mind is not thereby changed, and one's bodily, verbal, and mental actions do not change as a result of that observation, then the so-called observation is not observation at all, but conjecture and speculation. Conjecture and speculation are all modes and methods of thinking of the mind consciousness; they do not involve the manas, and what is conjectured and speculated has no effective force, and will not in the least purify the mind or transform one's bodily, verbal, and mental actions.