America is built on representative government and capitalism, two institutions that recognize how fickle human beings can be.

The marketplace of ideas we call politics and the marketplace of products we call free enterprise both assume that people are pliable creatures, likely to change their minds in a hurry. We honor choice as a national birthright.

But the country’s freedom is protected by men and women who give up a world of choices so that we can continue to have ours. They are the Americans who serve in our military, a call to service that doesn’t indulge inconstancy or caprice. They deserve our honor this Veterans Day — and every Veterans Day.

One cannot easily opt out once a commitment to military service is made. And when the battle is joined, we ask brave men and women to risk their lives — yes, their very lives — to defend this nation’s interests. It’s not a sacrifice that can properly be undertaken on a whim, shaped by the latest poll numbers or focus groups.

That’s why those long rows of white tombstones at our nation’s military cemeteries are such a striking part of the American landscape. They demonstrate, in a country touched by flux and equivocation and the endless mutability of opinion, that there have always been warriors who embrace principle as a fixed star, not a fashion statement.

Tiny American flags bloom from those cemeteries every Memorial Day, the day we set aside to honor the nation’s war dead. Veterans Day recognizes the veterans yet with us — the ones we can still find in our neighborhoods, our churches, the grocery store. America is blessed by the presence of these veterans in our civic life. They bear living witness not only to the privilege of liberty but its costs.

Not all members of the military see battle during their service, but there are other costs in serving in America’s armed forces. The profound pain of separation from family, the loss of privacy, the boredom — these are no small things. It is right and good that we should acknowledge those sacrifices each November, as the holidays approach. This Thanksgiving and yuletide season, as in every year, soldiers and sailors and airmen will be serving far away from home.

Today, we pause, in a month marked by gatherings for gratitude, to say thanks to our veterans. Their contributions are easy to overlook, but we forget their service at our peril.