IN the climactic moment of John Michael McDonagh's film Calvary (Salisbury Arts Centre, November 14), Chris O'Dowd's character tells the priest he didn't kill his dog but wants to know if it made him cry. The priest answers 'yes' quickly and easily. To the next question, whether he also had cried for all the children who were abused by priests, there was a long pause as the priest considers this life-or-death challenge. He then answers honestly.

The scene highlights so beautifully how grief and sorrow aren't linked in direct lines to the magnitude of sadness and hardship or to the degree of vulnerability and innocence of those who suffer injustice. My own tears on Remembrance Day were for the death of a friend's mother that morning and of our family cat in the afternoon – and then, not so much tears as sobbing.

I felt moved, sad and sombre about all those who have died in war but was dry-eyed through everything I saw and read in last week's coverage of the 100th anniversary of the First World War.

The fickleness of emotional response is never more clear to me than when I succumb to the worst examples of manipulative and false sentimentality, and this time of year, both are rife.

Cue the cheesy Christmas advertisement and in my head (well, I have been known to do this out loud as well) I am having a rant. John Lewis must be joking. A little boy playing matchmaker, giving his stuffed penguin another stuffed penguin to love? And then there's the mother, catching the scene and smiling beatifically at her sweet, adorable son?

Excuse me while I retch I think (or more likely, shout), but only after a little heartstring is pulled without my consent and to my utter dismay. Tis the season to brace ourselves for the onslaught of the commercial exploitation of sentiment. Every cliché of happy families, loving couples and cherished friends will be trotted out in the hope that it will inspire us to buy more stuff. We all know that buying things for people we love and showing them love are often very different but it's easy to get drawn into the conspiracy of commercialism. Just how easy is already abundantly clear.

John Lewis's £7m marketing campaign which includes this advertisement, soft toys, a smartphone app and penguin dens in stores has paid off: online stocks of Monty and Mabel penguins have sold out, apparently. Ho ho ho.