If you must use a door analogy, your sign would actually read "Party inside. Please join us!" with a bowl full of keys sitting beside the door. Now imagine if

If you must use a door analogy, your sign would actually read "Party inside. Please join us!" with a bowl full of keys sitting beside the door. Now imagine if each key is valid for only five openings of the door. When someone comes back to your place for a sixth time and their key doesn't work anymore, is it really reasonable to be upset if they choose another key from the bowl?