-Desire causes suffering.
The biological root of desires is our limbic system which is a common system shared between animal and human. If we're not mindful, we will be like a puppet controlled by the limbic system and it leads to suffering. It's a system responsible for basic instinct. A key factor in the limbic system is the neurotransmitter: dopamine.It causes all kinds of craving. If the limbic system is stimulated by external forces, our will can not control our action. For example, if one do cocaine, sooner or later one will become addicted. Thus, the purpose of buddhist precepts is as a prevention for falling into traps.
