We know joy when we are happy to take from life what is given. When we experience the joy of the soul and higher states of consciousness, this joy is the essence of completion and fulfillment. There is nothing that can add to it or take away from it. Joy is our natural state.
The mind thinks of the self as separate, the heart knows better. As one great Indian master, Sri Nisargatta, put it, "The mind creates the abyss, and the heart crosses it."