All living creatures naturally make their own cannabinoids, called endocannabinoids, inside their own bodies. The reason we make our own endocannabinoids is simple; to bind to receptors in the ECS to maintain homeostasis and improve health and happiness.  For example, when our body makes less THC or CBD than it needs to stay in balance, our health suffers, unless we satisfy the ECS with cannabinoids from the cannabis plant.