7 Reasons Why Scifi Book Series Outstay Their Welcomes

io9.com — Why do so many amazing novels sprawl into so-so trilogies? Let alone blah tetralogies, or dull ten-book series? Blame "Herbert's Syndrome," in which a great writer gets tempted to keep writing about a popular universe, like Frank Herbert's "Dune," long after its expiration date. Here's a handy guide to the symptoms and causes of Herbert's ailment