(CNN)As a physician, I have helped to care for many patients and families whose lives have been turned upside down by serious illnesses and injuries.
In the throes of such catastrophes, it can be difficult to find cause for anything but lament.
Yet Thanksgiving presents us with an opportunity to develop one of the healthiest, most life-affirming and convivial of all habits -- that of counting and rejoicing in our blessings.
Research shows that grateful people tend to be healthy and happy. They exhibit lower levels of stress and depression, cope better with adversity and sleep better. They tend to be happier and more satisfied with life. Even their partners tend to be more content with their relationships.
Perhaps when we are more focused on the good things we enjoy in life, we have more to live for and tend to take better care of ourselves and each other.
When researchers asked people to reflect on the past week and write about things that either irritated them or about which they felt grateful, those tasked with recalling good things are more optimistic, feel better about their lives, and actually visit their physicians less.
It is no surprise that receiving thanks makes people happier, but so does expressing gratitude. An experiment that asked participants to write and deliver thank-you notes found large increases in reported levels of happiness, a benefit that lasted for an entire month.
One of the greatest minds in Western history, the Greek philosopher Aristotle, argued that we become what we habitually do. By changing our habits, we can become more thankful human beings.
If we spend our days ruminating on all that has gone poorly and how dark the prospects for the future appear, we can think ourselves into misery and resentment.
But we can also mold ourselves into the kind of people who seek out, recognize and celebrate all that we have to be grateful for.
This is not to say that anyone should become a Pollyanna, ceaselessly reciting the mantra from Voltaire's "Candide": "All is for the best in this, the best of all possible worlds." There are injustices to be righted and wounds to be healed, and ignoring them would represent a lapse of moral responsibility.
But reasons to make the world a better place should never blind us to the many good things it already affords. How can we be compassionate and generous if we are fixated on deficiency? This explains why the great Roman statesman Cicero called gratitude not only the greatest of virtues but the "parent" of them all.
Gratitude is deeply embedded in many religious traditions. In Judaism, the first words of the morning prayer could be translated, "I thank you." Another saying addresses the question, "Who is rich?" with this answer: "Those who rejoice in what they have."
From a Christian perspective, too, gratitude and thanksgiving are vital. Before Jesus shares his last meal with his disciples, he gives thanks. So vital a part of Christian life is gratitude that author and critic G.K. Chesterton calls it "the highest form of thought."
Gratitude also plays an essential role in Islam. The 55th chapter of the Quran enumerates all the things human beings have to be grateful for -- the sun, moon, clouds, rain, air, grass, animals, plants, rivers and oceans -- and then asks, "How can a sensible person be anything but thankful to God?"
Other traditions also stress the importance of thankfulness. Hindu festivals celebrate blessings and offer thanks for them. In Buddhism, gratitude develops patience and serves as an antidote to greed, the corrosive sense that we never have enough.
Roots even in suffering
In his 1994 book, "A Whole New Life," Duke University English professor Reynolds Price describes how his battle with a spinal cord tumor that left him partially paralyzed also taught him a great deal about what it means to really live.
After surgery, Price describes "a kind of stunned beatitude." With time, though diminished in many ways by his tumor and its treatment, he learns to pay closer attention to the world around him and those who populate it.
Reflecting on the change in his writing, Price notes that his books differ in many ways from those he penned as a younger man. Even his handwriting, he says, "looks very little like that of the man he was at the time of his diagnosis."
"Cranky as it is, it's taller, more legible, and with more air and stride. And it comes down the arm of a grateful man."
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A brush with death can open our eyes. Some of us emerge with a deepened appreciation for the preciousness of each day, a clearer sense of our real priorities and a renewed commitment to celebrating life. In short, we can become more grateful, and more alive, than ever.
When it comes to practicing gratitude, one trap to avoid is locating happiness in things that make us feel better off -- or simply better -- than others. In my view, such thinking can foster envy and jealousy.
There are marvelous respects in which we are equally blessed -- the same sun shines down upon each of us, we all begin each day with the same 24 hours, and each of us enjoys the free use of one of the most complex and powerful resources in the universe, the human brain.
Much in our culture seems aimed to cultivate an attitude of deficiency -- for example, most ads aim to make us think that to find happiness we must buy something. Yet most of the best things in life -- the beauty of nature, conversation and love -- are free.
There are many ways to cultivate a disposition of thankfulness. One is to make a habit of giving thanks regularly -- at the beginning of the day, at meals and the like, and at day's end.
Likewise, holidays, weeks, seasons and years can be punctuated with thanks -- grateful prayer or meditation, writing thank-you notes, keeping a gratitude journal, and consciously seeking out the blessings in situations as they arise.
Gratitude can become a way of life, and by developing the simple habit of counting our blessings, we can enhance the degree to which we are truly blessed.