The black and white halves of the Yin-Yang symbol are similar to the two sides of a coin. They are different, and distinct, yet one could not exist without the other. The circle itself - which contains these two halves - is like the metal of the coin. It is what the two sides have in common - what makes them "the same."
Yin Yang personality types, signs of excess, foods and activities to correct the excess, plus interactive test to help determine your type. Based on Chinese traditional medicine and Korean Sasang (four body types) medicine.
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)