From The Gift, by Lewis Hyde:
I would like to speak of gratitude as a labor undertaken by the soul to effect the transformation after a gift has been received. Between the time a gift comes to us and the time we pass it on, we suffer gratitude. Moreover, with gifts that are an agent of change, it is only when the gift has worked in us, only when we have come up to its level, as it were, that we can give it away again. Passing the gift along is the act of gratitude that finishes the labor.