Why people like to see consistency, not sudden changes.
A woman asked me to dance last night.
"You're that writer chap who does the thing about dancing, aren't you?" she said delivering a certain force to the head of the nail. I decided to disagree.
"I see myself more as a philosopher," I said.
"What does a philosopher do?" she enquired.
“The philosopher is a man who says ‘All right,’ and goes to sleep in his armchair.”
“But you're on the dance floor," she said.
"Yes," I agreed. "Perhaps that's not my profession after all."
She looked at me oddly and then walked off, and that little exchange reminded me that by and large people expect us to be consistent. If we suddenly change, it can be very confusing.
The same applies to advertising. If you promote your company as one that sells quality products and then you suddenly claim you are the cheapest or suggest that everything is available at a discount, people will become confused.
That is not to say that you cannot change your advertising, moving for example from a descriptive style to one that opens with an interesting question. But rather it suggests to me that the underlying personality of the business should not change too much - or at least not very often.
You can be a firm that offers low cost products, or high quality products, or a wide choice of products, or an incredibly helpful service, and you can even combine a couple of these. But it can affect sales negatively if you jump suddenly from one to another in your advertising.