The words are usually used in reply to questioning the client as to what is the one thing customers should take away from their company's advertising.
Most of the time they seem to misunderstand (or more likely ignore) the relevance of the word 'one'. After all, why do they have to remember one thing when they can remember three (the answer is you'll be very lucky if they remember just the one but that's for another blog post...)?
If you're doing a price promotion just stick to a pound sign and why it offers the reader great value - keeping it simple. There's no need to mention low floors, wi-fi and your support of a local charity. Unfortunately, for that reason, there's lots of work in the industry (and others to be fair) that is just too busy.
Because 'there's space on the ad' doesn't mean you have to fill it with information that dilutes the one really important message you need customers to remember.
So let's strip things back to a core message and keep it simple - because anything other than a single ball at a time is really hard to catch.
Don't believe me? Ask your customers to try it and see how they get on.