Answer to quick quiz

The "Make airline reservations" item in the Upcoming Stuff notepad will have the same subitem, "American Airlines Flight 222" that the item shows in the tickler.

Even though the folder in which you added the subitem (the To-Do's) folder is not the same folder as the San Francisco Trip folder that you have in the Upcoming Stuff notepad, it's the same item in both folders. Any change you make to the item in one folder is automatically and immediately reflected in every folder to which the item is assigned.

A subitem belongs to its parent item, so adding a subitem in one folder is in effect making a change to the item (by giving it a "child" item) - and, therefore, the new subitem is shown in every folder to which the parent item. Is assigned.