Any room that has a choice that doesn't lead anywhere has a loose end. These loose ends are what allow you to continue your story or add onto other people's stories. When a story has no loose ends it is considered "Finished" since no rooms can be added to it.

You can find all your loose ends in a story you wrote by selecting the "Loose Ends" link in the "Administration" section of the story sidebar. This brings up a list of all the loose ends in your story and gives you links to both the loose end themselves and the rooms they are connected from.

You can clear up a loose end by making it connect to something, either creating a new room or linking it to an old room. Clicking on the loose end link will attempt to open the create new room page and let you do just that. If you are not logged in or don't have writing access rights in the story it will tell you that instead of allowing you to remove the loose end.