You have just landed on earth from another galaxy. (Come on, role play.) Your ship’s pre-programmed navigation coordinates meant you should have touched down in Washington, the capital of the planet.

But instead you are standing on a high street somewhere in England. In front of you is a primitive digital device set into a hole in a wall.

Above it there is a sign that says: FREE CASH WITHDRAWALS. You think to yourself, “Oh wow! Free money!”

Well, you’ll be thinking, what a wonderful place earth must be. You need cash? Tap, tap, tap, tap. Press the button, you’ve got it. Free and for nothing.

Yes, if only.

Apart from galactic visitors, there’s another far more complicated and intelligent life form that must find ATMs puzzling. Small children. They see us go to the cash machine, they see the cash come out. So why can’t they have a new bike? (Or more likely, a new PS3).  It’s no good telling them you’ve got no money. There’s a hole in the wall giving it away.

Here’s the problem. Some premises – and promises – assume that the reader will know what is really meant. Headlines that presume readers will somehow automatically understand the real meaning behind the words used, for example.

In reality, that’s very rarely the case. So you need to be careful not to lead people on with an attention-grabbing headline, only to let them down when it gets to the small print. Readers will forgive you for over-delivering on a promise. But you’ll never be forgiven for under-delivering.