You've written a book, and you love how it turned out. You feel a strong connection to the characters, you know the setting like no one else. You've gotten some good reviews. So should you continue with the story? Should that book...become a series?
Sequels and Whatnot
When it comes to extending a story and adding extra books, my answer is almost always yes. I can't even tell you how many times I've asked myself, and the Heavens, why Margaret Mitchell didn't write a sequel to Gone With the Wind.