I have to credit a couple of friends for sparking a fantastic discussion about plot catalysts and story conveniences. The conversation centered around what the MacGuffin of The Hobbit was.
First though, let's discuss what a MacGuffin is. Actually, let's hear what Alfred Hitchcock says it is:
According to Hitchcock then, a MacGuffin can be an item that may be fairly inconsequential to the story itself but provides motivation for the story characters. It can simply be an end point and not an active participant in the story. In a sense, it's the rail that keeps everything moving forward steadily. To use a Hitchcock movie as an example, let's talk Psycho.
Spoilers will follow, but Psycho was made over ten years ago so it's fair game. In the beginning of the movie, Marion - the leading lady - steals $40,000 from her employer. She goes to the Bates Motel and is murdered by the owner although he is unaware of the $40,000. Without that knowledge he buries the money hidden in her things along with her body and continues on. Meanwhile, Marion's employer begins a search for her because he wants the money. He involves Marion's family who in turn involves an investigator. Because of all these people being involved, Hitchcock now has an excuse to bring a cast of characters to the motel and begin his real story - the story of Norman Bates and his mother. After being gone for most of the movie, the concept of Marion and the $40,000 finally appears again but only at the final credits.
The $40,000 is the MacGuffin. It's not something the audience cares about all that much but is the central desire of most of the story's characters. A case can be made too that Marion is nothing more than a MacGuffin as well. In the end the desire to find the $40,000 and Marion was sufficient to involve multiple characters.
When we look at The Hobbit now with the understanding of what a MacGuffin is, it's easy to identify the treasure guarded by the dragon as the item that drives the story. It pushes all of the characters forward, keeps them on track, and enables Bilbo Baggins to pick up a very important ring for Tolkien's Lord of the Rings.
How to apply this concept to your manuscript? Your characters need depth and a MacGuffin is an excellent foundation, keeping the characters - and readers - grounded. As your characters develop and become more than static names, you may end up with a completely different character by story's end. Your readers need a constant reference point just as your characters need to be held to the storyline - your answer is the MacGuffin.
What other examples of MacGuffins can you think of?