What drives the Wheel of Life? Traditional depictions of the Wheel show three animals at the hub—a cock, a snake and a pig—each biting the tail of the one in front. These three animals represent craving, aversion and delusion, and their chasing one another around and around drives the Wheel. Craving, aversion and delusion make the world go round—they are the root cause of our un-Enlightenment and, according o the Buddha, the source of all suffering.
Craving is the desire to possess things that you like, and to include them in your ego-identity in the hope of getting a sense of security from having them as part of you. Aversion is the fearful, angered wish to get rid of things which you dislike and to exclude them from your ego-identity in the hope of attaining a sense of security from not having them as part of you. And delusion is the refusal to learn anything that you feel might threaten your ego-identity and upset the sense of security you try to get from it.
Enlightenment, according to the Buddha, consists in the complete eradication of these three unwholesome roots. This is a demanding task. Fortunately, the unwholesome roots are not the whole of our experience. We are also motivated by the three wholesome roots: generosity, kindness and wisdom
[...from Mindfulness and Money: The Buddhist Path of Abundance by Kulananda and Dominic Houlder, pg. 39-40]