The Yin Yang symbol is probably the strongest symbol ever designed because it says so much. It talks of the duality of life, difference and separateness yet also oneness. Above all it talks of balance which is the essence of Taoism from where the Yin Yang symbol comes.
Duality and Oneness
There is no light without darkness, up without down, hard without soft, one implies the other and one gives meaning to the other. The Yin Yang symbol perfectly describes the difference between the two opposites but also their connectedness. They are intrinsically joined together, they need each other to exist, they are in fact one. The key to a successful life is finding a balance between the principles of negative and positive, male and female, give and take, push and pull, passive and active etc.