To begin a narrative is to condemn it to an ending

While I do agree with ewx, I actually don't agree with the original sentiment - there are many good, well-written narratives where, at the end of the book, there's a natural conclusion to one story and another one starts without the author being committed to writing about it. Just because the characters have moved offstage that doesn't mean their tales are over, just that the writer has told the part of their story that's immediately relevant.