Like when you've orderd 
                    a take-away for delivery from your local Chinese, or Indian, 
                    or whatever - should you stand around, hovering by the front-door 
                    waiting for the delivery guy to turn up at the door and then 
                    open-up before he reaches your doorbell? Or should you wait 
                    until he has created a racket knocking on the door before 
                    you get up and open up?