(Note: This section pertains to the original version of the book instead of the 25th anniversary edition that dabbles in the fictionalized sequel.)
"I'm not trying to make this a downer, understand. I mean, I really do think that love is the best thing in the world, except for cough drops. But I also have to say, for the umpty-umpth time, that life isn't fair. It's just fairer than death, that's all" (8.206).
There have been lots of last-second miracles in this book that have allowed all of our favorite characters to survive. But to the bitter end, the narrator wants to remind us that life isn't always fair and not everyone gets a happy ending. The truth is that he doesn't really believe in happily-ever-after, even though he's telling us a fairy tale.
Morgenstern ends The Princess Bride with a cliffhanger, and we're not really sure what happens to our heroes. Maybe they get caught by Prince Humperdinck; maybe they survive and go on to lead super boring and disappointing lives. It's hard to tell, and even though Goldman ends by affirming that love is awesome, he's not willing to give us the warm and fuzzy feeling we're looking for. This book may be indebted to fairy tales, after all, but it also breaks the mold a bit, and the ending is one of the ways in which this happens.