It is a widespread misconception that a slogan has to be short to be catchy: in fact, a few extra words are often required to create a striking rhyme or rhythm – for example, it would have been quicker for FedEx to adopt the one-word tagline βOvernightβ, but opting for the longer βWhen it absolutely, positively has to be there overnightβ gave the tag its memorable turn of phrase. The line also captured the emotional state of the package-sender – a desire for certainty.
Excerpt from: 100 Ideas That Changed Advertising by Simon Veksner