The number, 3, is a unique number. It is the smallest balanced number, a rigid number from which one can begin to form an enclosed shape, most notably a triangle. This triple concept is very useful for structuring storytelling (beginning, middle, end) and enhancing the story making it inherently more satisfying or effective. Interestingly enough, you will also see many myths, legends, or religions in our world that involves trinity as opposed to a simpler, yet complex dual system, such as yin and yang.
Ephemeral Dreams 