Maguffins

In fiction, a MacGuffin (sometimes McGuffin or maguffin) is a plot device in the form of some goal, desired object
 The specific nature of a MacGuffin may be ambiguous, undefined, generic, left open to interpretation, or otherwise completely unimportant to the overall plot. The most common type of MacGuffin is an object, place or person the exact details of which are not integral to the narrative. However, a MacGuffin can sometimes take a more abstract form, such as money, victory, glory, survival, power, love, or even something that is entirely unexplained, as long as it strongly motivates key characters within the structure of the plot. Whether the audience should care about or identify with a MacGuffin in a story is open to debate among producers of fiction.
The MacGuffin technique is common in films, especially thrillers. Usually the MacGuffin is the central focus of the film in the first act, and then declines in importance as the struggles and motivations of characters play out. It may come back into play at the climax of the story, but sometimes the MacGuffin is actually forgotten by the end of the story.

In North by North West the maguffin is the drugs being smuggled via a statue.

The most famous MacGuffin of all time, the question driving Orson Welles' 1941 masterpiece Citizen Kane was what newspaper tycoon Charles Foster Kane meant by his deathbed utterance, "Rosebud." Although it's now widely known, the revelation that this MacGuffin was a symbol of Kane's lost childhood still packs a punch
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In Reservoir Dogs the diamonds are the Maguffin. At the centre of that unseen robbery and all its horrible, horrible consequences is a bag of diamonds. Rarely seen and barely mentioned, the diamonds are the impetus for all the swearing, fighting, shooting, killing, torturing, and backstabbing. Things get so horrific that audiences can be forgiven if they forgot that the bag of diamonds are what brought the colour coded madmen together in the first place. And in the end, every one of them (except for Mr. Pink) ends up dead for the MacGuffin.