Unless you’ve been living under a rock for the last week, it will not have escaped you that the Christmas season is upon us. The big retailers are ringing the bells to say “it’s here, it’s launched”. John Lewis, as part of its annual tear-fest, has given us Monty the Penguin. M&S has Christmas fairies spreading festive kindness far and wide. Sainsbury's has pulled out the big guns for their First World War truce. No doubt there are more ads to come.But what is it about these ads that captures our attention and makes them so heart-warming that people up and down the country find themselves wiping away a tear?