In his lecture at the British Film Institute, playwright and screenwriter David Hare offered some tips for screenwriting success. One was: make outcome movies rather than proposition movies.
A proposition movie or novel is one that sets up a great "what if" premise. For instance, what if a man wakes up one morning and discovers that everyone around him is a stranger--but they claim to be his friends and family? Interesting idea, right?
The problem is coming up with an equally great outcome. We've all seen lots of movies that start out really intriguing us, only to feel let down when the facts are revealed. The worst solution is "It was all a dream."
What Hare means by an outcome movie is one in which the ending is at least as amazing or interesting as the beginning. He said, "The end is what I think about first. If you get the ending right and you know where you're going, and that place is good, you can't go wrong."
Too bad the people behind "Lost" didn't do that.
Not only do you have to have a good ending in mind, along the way you have to drop enough clues to keep people interested (rather than confused). "Lost" continually added weirdness to the mix, but not the feeling that we were heading toward a coherent conclusion.
The same fate befell "Flash Forward"--even more so, since it was cancelled long before reaching whatever ending they had in mind. As of this writing, it's too early to tell whether "The Event" will go the same route.
This doesn't apply only to science fiction stories, it is of equal concern when writing in other genres, especially romantic comedies, where usually we know the general outcome--boy gets girl or girl gets boy (or any other mix of genders)--so it had better have something extra if it's going to stand out.
Endings are difficult. You'll find any number of people who will tell you they have a great idea for a movie, when all they really have is a great idea for a beginning. It's the professionals who know how to grow that opening into a story that will be as good in its last five minutes as in its first thirty.
(For tips on building great stories, see my book, "Your Writing Coach," available from Amazon and other online and offline booksellers. There's more information at www.yourwritingcoach.com)