ying/yang-opposite or contrary forces yet interconnected and interdependent in the natural world as they interrelate to one another. Many natural dualities are thought of as physical manifestations of the yin-yang concept.
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.
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)