"Always leave them wanting more" is often called the first rule of show business, and it's good advice for any director, actor or author.
When JK Rowling announced last week that she would unveil her next project, expectant fans started setting up online petitions asking - sometimes demanding - her to write an eighth Harry Potter book. Never mind that the saga came to a much-trumpeted end in print ... and the last book is being drawn out into two interminable movies.
Of course, these same rabid fans baying for more will be the same ones who savage their heroes if the latest instalment does not meet their inflated expectations.
How many franchises have been ruined because their creators did not know when to walk away? For many fans, the Star Wars legacy has been ruined by the derided second trilogy (The Phantom Menace, Clone Wars and Revenge of the Sith) that George Lucas unleashed on the public at the end of the last century. Even the critically adored Godfather and Godfather II were lumbered with a third instalment that disappointed many. And don't even get us started on Rocky at age 60.
Rowling's Harry Potter opened a new universe, especially for young readers, but it's time for someone else to make the magic.