"One wolf represents fear, anger, envy, sorrow, regret, greed, arrogance, self-pity, guilt, resentment, inferiority, lies, false pride, superiority, and ego.
"The other stands for joy, peace, love, hope, sharing, serenity, humility, kindness, benevolence, friendship, empathy, generosity, truth, compassion, and faith.
"This same fight is going on inside you, and inside every other person, too," he added.
The grandchildren thought about it for a minute and then one child asked his grandfather, "Which wolf will win?"
The grandfather simply replied, "The one you feed."
Source: I had heard this story years ago and recently found it on Deb Wilson's great blog: The British Homemaker.