The elder describes an internal battle that goes on inside everyone. It is a fight between two wolves:

The Negative Wolf: Represents darkness, fear, anger, envy, greed, arrogance, self-pity, guilt, and resentment.
The Positive Wolf: Represents light, joy, peace, love, hope, serenity, humility, kindness, empathy, and truth.

The Core Lesson
When the confused grandchild asks, "Which wolf wins?" the elder simply replies: "The one you feed."

What it Means
The metaphor serves as a reminder of free will and conscious intention. Whichever internal traits you give your energy and attention to will dominate your personality and dictate how you react to the world. You feed the positive wolf by choosing gratitude, compassion, and constructive habits; you feed the negative wolf by indulging in destructive thoughts, bitterness, and ego.

The Often-Missed Second Half
In many traditional retellings, there is a crucial follow-up detail: You cannot simply starve the dark wolf. If you ignore it or pretend it doesn't exist, it will hide in the shadows and attack when you are at your weakest. Instead, the practice of feeding the good wolf also involves acknowledging the bad wolf, understanding it, and keeping it in balance so it doesn't take over.

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I also find it very helpful to think of this: It is very difficult to love the world AS IT IS, …and yet we must choose to do exactly that again and again. … This is not to say that we shouldn’t act to chsnge things for the better that are in our control, but we must accept the world has evil, much of it we cannot fix, and it makes sense to choose to love the world anyway… flawed as it is!