A supermarket checkout line. Cheesy holiday music is playing overhead. Not the fun kind of cheesy music, but the kind once heard in Kmart á la 1973.

There is an old man at the head of our long checkout line, standing at the register. He digs through his pockets, but keeps coming up empty handed.

“I’m sorry, miss,” he says to the cashier. “I must’ve left my wallet at home.”

He is embarrassed, and the young cashier is unsure about what to do.

I am watching this entire exchange closely because I am a columnist who writes human interest stories.

We columnists must keep our observational reflexes honed as sharp as wiffle-ball bats. We have to stay ready because we are not real writers.

Writers are inspired artists and poets. Columnists are factory-line workers who take whatever stories they can get.

Your big-time writer is a person with incredibly poignant things to say about life and the profundity of the human condition; they have grand ambitions of someday winning a major literary award, and possibly having a “New York Times” best-smeller.

Whereas a columnist’s highest aspiration is for someone to cut his or her column out of the paper and hang it on the refrigerator.

So columnists have to work harder than true writers because we can’t rely on inspiration. Besides, our job is not to be inspired, but to constantly find new stories. This is not simple work. Therefore, most of the time you find me writing about key social issues such as, say, my dogs.

But the beauty of all this is, every once in a while a column will actually fall into your lap.

This is a rare thing indeed, and one of the most precious things that can happen to a stringer of words. Your task as a columnist is to be mindful enough to notice this pivotal moment is occurring, then to ignore it and keep writing about your dogs.

So anyway, after the old man in the cashier lane realizes he doesn’t have enough money, the old woman behind him in line does something remarkable.

She says, “You know what? Let me pay for it.”

I’m expecting the woman to lay down the exact amount of change to make up the difference the old man owes. Instead she surprises everyone by whipping out her Mastercard and paying his entire grocery bill.

“Merry Christmas,” she says.

Everyone in line is now smiling at each other. I’m smiling, too, because this column just wrote itself.

Now it’s the old lady’s turn to pay for her own groceries. But the guy in line behind HER steps forward and shoves his Amex into the card slot and pays HER bill.

“Just paying it forward,” he says. “Merry Christmas.”

This column has just graduated into a refrigerator-hanger

Next in line. When the cashier is scanning the next guy’s items, there is a young father behind him with a cart full of screaming babies and groceries.

Young Dad digs into his wallet and hands the cashier a gift card. The cashier scans the card. “Let’s keep this going,” says Young Dad, who has just bought a stranger’s groceries.

“Merry Christmas,” says Young Dad.

They shake hands, then slap each other’s backs for a man-hug.

I am going to win a Pulitzer.

The cashier says, “I’ve never had anything like this happen to me in my whole life. This is awesome. People are so kind.”

The young father blushes and says, “Well, I just didn’t want to break the chain. You know?”

After she scans his groceries, the cashier gives the total to Young Dad. At this point I am now stepping forward to offer to pay for this man’s items since (a) I am next in line, and (b) this will make a great ending to the column.

But the cashier beats me to it.

“No, wait!” the cashier says, excitedly plucking a debit card from her purse. “I wanna pay for your groceries, sir.”

So she pays for Young Dad’s groceries. They exchange handshakes and hearty Merry Christmases. And this is the most beautiful Yuletide moment I’ve seen in maybe my entire life. Say what you will about our species, but humankind will floor you with its goodwill. My heart is full.

Then it’s my turn at the register.

There is nobody behind me in line, nobody ahead of me. The cashier rings up my groceries then clears her throat loudly at me. The computer immediately makes a violent buzzing noise and the screen reads CARD DECLINED.

And now you know what it feels like to be a columnist.