the bond between two. one of light and the other of dark, one cannot live without the other. without light there is no dark, and without dark there is no light. there is bad and good in this world. the light of good in life cannot happen with out the darkness of the bad. the balance of the two is the most important. if there was no good the world would be plunged into the bad, and without the bad in the world, the world would be nothing but good. you think yes all the good would be a good thing, but too much of light would be a downfall because once there is too much good then nobody would truly live how they want. within the darkness there is a light, and within the light there is a darkness.