Why All Series Should Be Trilogies

A series should always be a trilogy. Who has ever heard of a du-ology? And bi-ology is something quite different. What about a quadrology? Pentology? Nope. Clearly if there is no word for it, it just can't be.

And trilogy is a versatile term. "The Hitchhiker's Guide to the Galaxy" is a four book trilogy. So is "Lord of the Rings," if you count "The Hobbit." Those are some successful quadrologies. The "Harry Potter" books are a septology, which doesn't quite sound as naughty as a sextology...