Oh, the wisdom of stories!!!
You can talk about good and evil, pontificate about ying and yang, try to explain the id and the ego. OR you can tell a story. This one is thanks to Carol Grever and her wonderful blog http://www.straightspouseconnection.com/2009/03/the-fight-inside-me.html
Also check out her books and film http://www.carolgrever.com
A grandmother is teaching her little granddaughter. She says, “Two wolves are fighting inside you. One of the wolves is hateful, angry, aggressive, envious, resentful, guilty, and despairing. The other wolf is compassionate, joyful, peaceful, loving, hopeful, serene, kind, generous, and forgiving. These two wolves are always fighting inside you.”
The little girl thinks about this image of opposites for a moment, then asks, “Grandmother, which wolf wins?”
The wise elder replies, “The one you feed.”