How to be fulfilled in life?

Many of us in life are happy, successful, and have excellent relationships, yet we do not feel fulfilled. We feel as if something is missing in life and we are even unable to figure out what it is.

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There is an unknown seeking, a quest within us that we cannot truly define, but it feels like a longing for something. It is almost like a pain and yet we do not know the basis of this pain. A great many people live through this experience of life and think that may be it is a quest to know oneself or to find a meaning or purpose of life.

So the question is what is fulfillment and how to find it?