Giving the reader permission to believe

Despite universal cynicism towards salesmen in general and ads in particular, there’s a part of us that really wants to believe we’ll have more and better sex if we use a certain aftershave or hair conditioner. Unfortunately that part is patrolled by a beefy armed guard who can easily wrestle inanities like this to the ground. What our beefy armed guard needs is enough supporting logic to accept your premise and not look like an idiot. DDB’s advertising for Avis didn’t just say Avis tried harder; it said when you’re only number two you have to - or else.