Then I had an idea!

Taking a giant leap forward, I was thinking about the ending. How does it end? What are the circumstances leading up to it? Is it a valid ending?
Then I had an idea: the ending itself, happening where it does, leaves unanswered questions. Questions so important that they demand a second book be written in order to arrive at the answers. Fantastic! I now have something tangible upon which to base a second book - and, just as important, there is always the possibility of a third book. Only veiled thoughts of the future have happened inside my head, but they are there, growing.
Perhaps, some day soon I hope, the idea upon which the third book is to be based will come to me.
I do know that there doesn't have to be a third book, nor even a second. It's the quality that counts, not the quantity. At the very least for me. Just I always have to explore the possibility of future works.
Getting there...