The Things That Sentient Beings Rely On Are All Unreliable.

The supreme faculty (indriya) is located in the back of the brain, and it is the place where mental dharmas and material form are connected. When the four great elements of the supreme faculty fall into disharmony—such as cerebellar atrophy and degenerative brain disease—the resulting impairments of movement, cognition, and memory all arise from the aging and deterioration of the supreme faculty. When the mental dharmas of the six consciousnesses cannot function and arise normally, sentient beings can easily die. Both cerebral hypoxia and cerebellar atrophy can destroy the supreme faculty and obstruct the arising of the six consciousnesses and their various cognitive activities. Human life is extremely fragile: if a single breath fails to come, it leads to cerebral hypoxia and brain death, bringing life to an end. Why is it that practicing deep breathing makes it easy to attain meditative concentration (samādhi)? Deep breathing ensures the supply of oxygen to the brain and benefits physical health. When the brain is unobstructed and the mind consciousnesses of the six consciousnesses are comfortable, one no longer needs to struggle against or alter the physical body, and thus it becomes easy to attain concentration.

From this we can see that the functions of the five aggregates (pañca-skandha) are of dependent origination (paratantra) and cannot be autonomous. They cannot stand on their own; they are extremely illusory and unreal. Relying on so many external conditions just to have normal activity of the five aggregates—if even one condition is lacking, it will not work—such a body of the five aggregates is extremely unreliable and far too insubstantial; therefore none of it is the self. The things sentient beings depend upon are all unreliable. If one could manage to depend on nothing at all, then one would be fearless. It would be wonderful if in the future we could cultivate to the point of not relying on any external environmental conditions, so that impermanent things would no longer have any effect on us; at that point one would be almost immortal, which, it is estimated, would require attaining the eighth bhūmi or above. We should pursue and rely upon a reliable, unchanging dharma of permanence that does not require external conditions.