In Chinese philosophy, the concept of yin-yang, which is often called "yin and yang", is used to describe how seemingly opposite or contrary forces are interconnected and interdependent in the natural world; and, how they give rise to each other as they interrelate to one another. Many natural dualities(such as male and female, light and dark, high and low, hot and cold, life& death, and so on) are thought of as physical manifestations of the yin-yang concept.
The world isn't separated into the good and the bad. There is good and bad in all of us. It is the part we chose to act on that makes us who we are. (And yes Harry Potter fans this is a not completely correct quote from Harry Potter)
The yin-yang is one hell of a concept, don’t you think? Not only does it show us that we can’t have the good without the bad, but that we can’t have the bad without the good. No matter if it’s good or bad, black or white, day or night, dark or light - Both are important, both are needed.