"Prior to realization, the individual's true nature is obscured by the root ignorance that gives rise to the conceptual mind. Ensnared in dualistic vision, the conceptual mind divides the seamless unity of experience into conceptual entities and then relates to these mental projections as if they inherently exist as separate beings and things. The primary dualism divides experience into self and other, and from the identification with only one aspect of experience, the self, preferences develop. This results in the arising of aversion and desire, which become the basis for both physical and mental actions. These actions (karmas) leave traces in the individual's mind as conditioned tendencies, resulting in more grasping and aversion, which lead to new karmic traces, and so on. This is the self-perpetuating cycly of karma."
in The Tibetan Yogas of Dream and Sleep, de Tenzin Wangyal Rinpoche