Handing my daughter thank-you notes and stamps the other day, I found myself reflecting on this habit of saying thanks in writing. When I was a kid, my father's mother used to make gifts to me of stationery and stamps. Invariably, she received the first sheet out of the box in a thank-you note and the latest on school, the family, the dog, whatever else seemed vitally important to me to share.

So it went to with my mother's mother. After these women died, I received back envelopes full of my correspondence to them. Since I kept all their letters, I have our complete conversations to return to from time to time and to share with my daughter.

These conversations--indeed, these relationships--were founded on gratitude, the notion that you notice, reflect on, and express appreciation for the kindnesses that come your way. To the persons who make gestures that are expressions of love, you give back a few minutes of your time to say "I love you back" in the form of "thanks."

It's a lovely thing that the single United States holiday that every citizen can share is Thanksgiving Day. Whatever about the land grabbing of 400 years ago, we can think here and now about all the things that come our way that are good. Our souls depend on it.

This is an old open and universal secret. The Psalms are full of songs of gratitude to God, for example. The Buddha taught gratitude as a way of being. He taught that we must recognize that we cannot live in selfish isolation. Rather, we coexist in this immense world with many people, animals, and things to whom we owe our gratitude because they make our lives possible each day.

This seems so simple, yet some people can't manage it. Some, Regina Sara Ryan says in Praying Dangerously, find gratitude to be terrifying: "The wonder of a moment in which there is nothing but an upwelling of simple happiness is utterly awesome. Gratitude is so close to the bone of life, pure and true, that it instantly stops the rational mind, and all its planning and plotting. That kind of let go is fiercely threatening. I mean, where might such gratitude end?"

Researchers on the nature, causes, and effects of gratitude Robert A. Emmons (University of California, Davis) and Michael E. McCullough (University of Miami) have found that "grateful people report higher levels of positive emotions, life satisfaction, vitality, optimism and lower levels of depression and stress. The disposition toward gratitude appears to enhance pleasant feeling states more than it diminishes unpleasant emotions. Grateful people do not deny or ignore the negative aspects of life."

Further: grateful people are more likely to be empathetic, helpful, generous, and able to see things from others' perspectives.

Best of all: "grateful people are more likely to acknowledge a belief in the interconnectedness of all life and a commitment to and responsibility to others."

All of that is definitely worth the price of a few stamps. And the letters come back.