From "Gratefulness, the Heart of Prayer," by Brother David Steindl-Rast:
Ordinary happiness depends on happenstance. Joy is that extraordinary happiness that is independent of what happens to us. Good luck can make us happy, but it cannot give us lasting joy. The root of joy is gratefulness.
We tend to misunderstand the link between joy and gratefulness. We notice that joyful people are grateful and suppose that they are grateful for their joy. But the reverse is true: their joy springs from gratefulness. If one has all the good luck in the world, but takes it for granted, it will not give one joy. Yet even bad luck will give joy to those who manage to be grateful for it.
We hold the key to lasting happiness in our own hands. For it is not joy that makes us grateful; it is gratitude that makes us joyful.