The Buddha clarified the two causes for being upside down, in detail

I2 He clarified the two causes for being upside down, in detail.
J1 He makes it clear that living beings are upside down.
K1 From the true they give rise to the false.

Sutra:

Ananda, what is meant by the upside-down state of living beings? Ananda, the reason that the nature of the mind is bright is that the nature itself is the perfection of brightness. By adding brightness, another nature arises, and from that false nature, views are produced, so that from absolute nothingness comes ultimate existence.

Commentary:

Ananda, what is meant by the upside-down state of living beings? Ananda, the reason that the nature of the mind is bright is that the nature itself is the perfection of brightness. The basic nature is perfectly bright and illumines all appearances. But by adding brightness, another nature arises. By adding brightness to the inherent brightness of the self nature, another nature comes into being, that of karmic obstructions. This is because from the true the false arises. Based in the nature of the treasury of the Tathagata, one gives rise to ignorance. Another way of putting it is that one tries to add brightness to enlightenment when all along the nature of enlightenment is brightness itself. In that one movement of the false thought to add light to brightness, the appearance of karma is created, the first of the three subtle appearances.

And from that false nature, views are produced. This is the appearance of turning. Originally there was the nature of the treasury of the Tathagata, but now ignorance has arisen. Ignorance is a kind of delusion, and once there is delusion, a lack of clarity, then karma arises. The nature of that karma is false, and from it views arise. Birth and death come into being.

From a single unenlightened thought
the three subtle appearances arise.
Then external states become the conditions
for the arising of the six coarse appearances.

This concept was also discussed earlier in the sutra. When falseness arises from within the truth, then the appearance of karma is produced. With the appearance of karma, there comes the appearance of turning. First one gives rise to delusion, but then one creates karma and after that must undergo a retribution. So the last is the appearance of manifestation. These are the three subtle appearances:

1. the appearance of karma;
2. the appearance of turning;
3. the appearance of manifestation.

From this process, a great deal of confusion arises, which extends itself into the six coarse appearances:

1. the appearance of knowing, which refers to worldly knowledge;
2. the appearance of continuation, in which things go on and on without cease;
3. the appearance of attaching and grasping;
4. the appearance of reckoning names;
5. the appearance of the arising of karma;
6. the appearance of the suffering of being bound by karma.

So that from absolute nothingness comes ultimate existence. That is the third subtle appearance, that of manifestation. Because of the falseness, existence comes into being.

Sutra:

All that exists comes from this; every cause in fact has no cause. Subjective reliance on objective appearances is basically groundless. Thus, upon what is fundamentally unreliable, one sets up the world and living beings.

Commentary:

All that exists comes from this. "This" refers to ignorance, because:

From a single unenlightened thought
the three subtle appearances arise.
Then external states become the conditions
for the arising of the six coarse appearances.

"All that exists," then, refers to these appearances. Yet, every cause in fact has no cause. "Cause" here refers to a place of reliance. Why is there said to be no cause? It is because, although the three subtle appearances are said to arise from ignorance, ignorance is not really dependable. It is not a true place of reliance. Ignorance itself is a false creation, an empty appearance. Therefore, although it seems to be that the three subtle appearances arise out of ignorance, it doesn't really happen that way, because ignorance itself doesn't even exist! Since ignorance doesn't have any substance of itself, how can the three subtle appearances arise from it? Subjective reliance on objective appearances is basically groundless. Living beings are the subjective aspect that relies on ignorance, the objective aspect. But basically there is no foundation in this. There is really no source. Thus, upon what is fundamentally unreliable, one sets up the world and living beings.

Basically there is nothing to be depended on, but it is on this unreliable ignorance that the world is established. Out of what is empty, false, and unreal the world is set up, and with it all living beings. Their very existence is empty and false; there is nothing real about it.

K2 They confuse their origin so it is difficult to return.

Sutra:

Confusion about one's basic, perfect understanding results in the arising of falseness. The nature of falseness is devoid of substance; it is not something which can be relied upon.

Commentary:

Confusion about one's basic, perfect understanding results in the arising of falseness. "Confusion" refers to the arising of falseness out of truth. Basically there is no name or appearance in the nature of the treasury of the Tathagata. But when ignorance is produced, confusion results. Since one is confused, one no longer recognizes one's inherent enlightened nature. Once that happens, it is as if one has lost one's home. Then falseness arises. The nature of falseness is devoid of substance; it is not something which can be relied upon. Although falseness arises out of truth, falseness itself doesn't have any substance. It came out of truth, but it is merely illusory. Since ignorance doesn't have a substance of its own, the three subtle appearances cannot really be based on it.

Sutra:

One may wish to return to the truth, but that wish for the truth is already a falseness. The real nature of true suchness is not a truth that one can seek to return to. By doing so one misses the mark.

Commentary:

One may wish to return to the truth, but that wish for the truth is already a falseness. Basically, ignorance has no substance of its own, and as a consequence the three subtle appearances aren't really based on anything. Therefore, it is a mistake to decide that you want to "return to the truth," to go back to the source in order to seek for the truth. You've just given rise to more falseness. If you want to return to the truth, you should merely refrain from adding brightness to enlightenment; just don't add a head on top of a head. Don't go looking for a donkey while riding on a donkey.

The real nature of true suchness is not a truth that one can seek to return to. It's not that you decide to return to inherent truth. Rather, you simply dispense with ignorance; that itself is the truth. There's no need to seek further. The entire reason you do not grasp the truth is that you are possessed with ignorance. If you discover that ignorance has no substance, then "you don't get rid of false thinking, and you don't seek the truth." All you have to do is destroy ignorance, and the dharma nature manifests. By doing so one misses the mark. Basically one does not have to seek truth or cut off falseness. All one has to do is smash through ignorance, and one's enlightened nature appears spontaneously. But if one does not smash through ignorance and yet seeks the truth, one is doing what is called "letting go of the root and grasping at the branches." The first step is to break through ignorance. When ignorance is destroyed, the three subtle appearances also disappear, and so do the six coarse appearances. How can one seek truth when one has not destroyed ignorance? If one tries to do it that way, one ends up with more false appearances.

K3 They produce karma which brings a retribution.

Sutra:

What basically is not produced, what basically does not dwell, what basically is not the mind, and what basically are not dharmas arise through interaction. As they arise more and more strongly, they form the propensity to create karma. Similar karma sets up a mutual stimulus. Because of the karma thus generated, there is mutual production and mutual extinction. That is the reason for the upside-down state of living beings.

Commentary:

What basically is not produced refers to the ignorance which produces appearances. What basically does not dwell refers to karmic consciousness, which is to say the eighth consciousness. What basically is not the mind refers to the aspect of seeing. What basically are not dharmas refers to the aspect of appearances. Ignorance, karmic consciousness, and the aspects of seeing and appearances have no source and no substance of their own. Their very existence is illusory. Nonetheless, this sickness is contagious once it arises: that is what is meant by they arise through interaction. It is the same as the interconnection of the eyes, ears, nose, tongue, body, and mind. As they arise more and more strongly, they form the propensity to create karma. Their continual arisal and transformation become powerful, and, so similarly, the karma they make increases. Ignorance, karmic consciousness, and the aspects of seeing and appearances aid one another; they borrow strength from one another. This interaction becomes stronger and stronger until, when it reaches its peak, they become fused and create karma. Karmic obstacles arise. Similar karma sets up a mutual stimulus. Because of the karma thus generated, there is mutual production and mutual extinction. Because of this interconnection and mutual stimulation, production and extinction are created. That is the reason for the upside-down state of living beings. That's how living beings come to be and how they give rise to inversions.