Thanksgiving is about gratitude, which is a disposition, a virtue and a way of thinking all at once.
We often trivialize gratitude as little more than a passing feeling that gets expressed on greeting cards or in quick thank-you notes (although I'd make a strong case for thank-you notes, which I do not write enough of). We tend to cite courage, honor, compassion, truthfulness, loyalty and a long list of other attributes as being far more important in the panoply of admirable moral traits.
It can also be argued that gratitude is a privilege of those who have their health, enriching personal and family relationships, wealth, and the opportunity to live in peaceful and prosperous nations or neighborhoods.
But this is precisely where things get complicated, and why gratitude is a form of discipline. Often those with hard lives and little wealth express enormous gratitude for what they do have, sometimes simply for life itself. Perhaps those with the least best understand Rabbi Abraham Joshua Heschel's famous aphorism: "Just to be is a blessing. Just to live is holy."