The Buddha said: Since the time without beginning, all living beings have given rise to all sorts of inversion because of the karmic seed (of ignorance) which is like the aksa shrub(The aksa seed is threefold and so illustrates the simultaneous character of illusion, action and suffering). 
This is why seekers of the Truth fail to realize Supreme Enlightenment but achieve only (the states of) Sravakas(arhats), pratyeka-buddhas, heretics, devas and demons, solely because they do not know the two basic inversions, thereby practising wrongly like those who cannot get food by cooking sand in spite of the passing of aeons as countless as the dust. What are these two basic inversions? Ananda, the first is the basic root of birth and death caused, since the time without beginning, by the wrong use of a clinging mind which people mistake for their own nature, and the second is their attachment to causal conditions (which screen) the basically bright essence of consciousness which is the fundamentally pure and clean substance of Nirvanic Enlightenment. Thus they ignore this basic brightness and so transmigrate through (illusory) realms of existence without realizing the futility of their (wrong) practice.