The briefcase, the formula, the list of names. It works because pursuit is what generates the scenes, and the specific contents only matter to the people pursuing it. Hitchcock’s point was that the audience is invested in the chase and indifferent to the prize, which is why films that stop to explain the prize lose momentum.
The failure is treating a MacGuffin as a mystery. If a piece signals that the contents are the point, it has promised a revelation and now has to deliver one, and almost no revelation is as interesting as the anticipation of it. Choose one: an object that motivates, or a secret that pays off. Not both.
The commercial version is a product presented as the object of pursuit. It works when the pursuit is dramatised and fails when the film pauses to describe the product’s features, which is the exact move that converts a MacGuffin into an anticlimax.
What is a MacGuffin?
An object or goal that drives the characters’ actions and whose specific nature does not matter to the audience. Its function is to generate pursuit.
What is the difference between a MacGuffin and a mystery?
A MacGuffin motivates and is never explained; a mystery promises an explanation and must deliver one. Signalling that the contents matter converts the first into the second and creates a debt most stories cannot repay.