"At one time, the Buddha addressed the disciples thus: 'there is, O Bhikkhus, in the ocean a turtle, both of whose eyes are blind. He plunges into the water of the unfathomable ocean and swims about incessantly in any direction wherever his head may lead. There is also in the ocean the yoke of a cart, which is ceaselessly floating about on the surface of the water, and is carried away in all directions by tide, current and wind. Thus these two go on throughout an incalculable space of time: perchance it happens that in the course of time the yoke arrives at the precise place and time where and when the turtle puts up his head, and yokes on to it. Now, O Bhikkhus, is it possible that such a time might come as is said?' 'In ordinary truth, O Lord,' replied the Bhikkhus 'it is impossible; but time being so spacious, and an aeon lasting so long, it may be admitted that perhaps at some time or other it might be possible for the two to yoke together, as said; if the blind tortoise lives long enough, and the yoke does not tend to rot and break up before such a coincidence comes to pass.'
Then the Buddha said, 'O Bhikkhus, the occurrence of such a strange thing is not to be counted a difficult one; for there is still a greater, a harder, a hundred times, a thousand times more difficult than this lying hidden from your knowledge. And what is this? It is, O Bhikkhus, the obtaining of the opportunity of becoming a man again by a man who has expired and is reborn once in any of the four realms of misery. The occurrence of the yoking of the blind tortoise is not worth thinking of as a difficult occurrence in comparison therewith. Because those who perform good deeds and abstain from doing bad alone can obtain the existence of men and Devas. The beings in the four miserable worlds cannot discern what is virtuous and what vicious, what good and what bad, what moral and what immoral, what meritorious and what de-meritorious, and consequently they live a life of immorality and demerit, tormenting one another with all their power. Those creatures of the Niraya and Peta abode in particular, live a very miserable life on account of punishments and torments, which they experience with sorrow, pain and distress. Therefore, O Bhikkhus, the opportunity of being reborn in the abode of men is a hundred times, a thousand times harder to obtain than the encountering of the blind turtle with the yoke."
According to this Sutta, why those creatures who are born in the miserable planes are far from human existence is because they never look up but always look down. And what is meant by looking down? The ignorance in them by degrees becomes greater and stronger from one existence to another; and as the water of a river always flows down to the lower plains, so also they are always tending towards the lower existences; for the ways towards the higher existences are closed to them, while those towards the lower existences are freely open. This is the meaning of "looking down". Hence, from this story of the blind turtle, the wise apprehend how great, how fearful, how terribly perilous are the evils of the -- Puthujjana-gati, i.e. "the dispersion of existence."
What has been said is concerning the Puthujjana-gati. Now what is Ariya-gati? It is deliverance from the dispersion of existence after death. Or it is the disappearance of that "dispersion of existence" which is conjoined with the destiny of inevitable death in every existence". It is also the potentiality of being reborn in higher existences or in existences according to one's choice. It is also not like the fall of coconuts from trees; but it is to be compared to birds, which fly through the air to whatsoever place or tree on which they may wish to perch. Those men, Devas and Brahmas who have attained the Aryan state, can get to whatever better existence, i.e., as men, Devas, Brahmas, they may wish to be reborn into, when they expire from the particular existence in which they have attained such Aryan state. Though they expire unexpectedly without aiming to be reborn in any particular existence, they are destined to be reborn in a better or higher existence, and at the same time are entirely free from rebirth into lower and miserable existences. Moreover, if they are reborn again in the abode of men, they never become of the lower or poorer classes, nor are they fools or heretics, but become quite otherwise. It is the same in the abodes of Devas and Brahmas. They are entirely set free from the Puthujjana-gati.
What has been said is concerning the course of Ariyas. Now we will explain the two Gatis side by side. When a man falls from a tree he falls like a coconut because he has no wings with which to fly in the air. In precisely the same way when men, Devas and Brahmas who are Putthujjana, riveted to the hallucination of wrong views and having no wings of the Noble Eightfold Path to make the sky their resting-place, transmigrate after the dissolution of their present bodies into new ones, they fall tumbling into the bonds of the evils of dispersion. In this world ordinary men who climb up very high trees fall tumbling to the ground when the branches which they clutch or try to make their resting place break down. They suffer much pain from the fall, and sometimes death ensues because they have no other resting-places but the branches, neither have they wings to fly in the air. It is the same with men, Devas and Brahmas who have their hallucination of Wrong Views, when their resting-place of Wrong Views as regards self is broken down, they fall tumbling into the dispersion existence. For their resting- places are only their bodies; and they have neither such a resting place as Nibbána, nor such strong wings as the Noble Eightfold Path to support them. As for the birds, though the branches they rest on may break, they never fall, but easily fly through the air to any other tree. For the branches are not their permanent resting places but only temporary ones. They entirely rely on their wings and the air. In the same way, men, Devas and Brahmas who have become Ariya and are freed from the hallucination of Wrong Views, neither regard their bodies as their Attá or Self, nor rely upon them. They have in their possession permanent resting places, such as Nibbána, which is the entire cessation of all tumbling existence. They also possess the very mighty wings of the Noble Eightfold Path, which are able to bear them to better existences.
What has been said is concerning the distinction between the two Gatis, i.e., the Putthujjana-gati and the Ariya-gati.