Most of us believe that strong brands have a consistent promise and consistent values, articulated via a consistent communications idea. Many even believe that the best form of consistency is a so called 'campaign device'. You know you have got one of these when it is taken as read that each ad will feature a monologue from Jamie Oliver or a nodding dog replying 'Oh yes'.
Creative teams, on the other hand, tend to be lukewarm about these long-running creative contrivances. They like coming up with them, but hate sticking to them because they restrict creativity and make the communication predictable.
Specsavers doesn't have the restriction of a dog, or a celebrity. It is free from the binds of a creative device. In the past six months, it has treated us to a woman burning her turkey, a shepherd shearing his dog and a giant ear on the bus.
But that is not to say Specsavers is being inconsistent. As a challenger to established expensive competitors, it deploys an unswerving strategy centred on regret. It dramatises the foolishness of people who have made expensive mistakes buying their glasses elsewhere and 'should've gone to Specsavers'.
Given all that, Je ne regrette rien is not a surprising choice for Specsavers. Edith Piaf warbles on about having no regrets, other than missing out on Specsavers' latest two-for-one deal.
Its admirable performance at number two in this week's table is testimony to the consistent use of the regret strategy, and to the creative licence it has taken with it. More so, perhaps, than that it has taken here with Michel Vaucaire's lyrics.
The question is, however, whether the nodding dog's appearance some 13 recall points above it suggests Specsavers should shackle itself to a creative device after all.