How did a MacGuffin keep the plot moving in Alfred Hitchcock’s films?

In the films of Alfred Hitchcock, a MacGuffin serves as a narrative "springboard" that initiates the plot and keeps the audience engaged, even though the object itself is often trivial or vague.1

Hitchcock utilized the MacGuffin to build suspense by focusing on a goal that the characters on screen worry about intensely, while the audience remains largely indifferent to the object's specific nature. Because the characters are driven by the pursuit or protection of this item, they are forced into a series of precarious and suspenseful situations.123

For example, in The 39 Steps, the MacGuffin—top-secret military plans—propels the protagonist into a dangerous journey across Scotland. The audience continues to follow the story not because they are invested in the plans themselves, but because they are captivated by the protagonist’s attempts to escape the resulting predicaments. By keeping the MacGuffin’s significance deliberately vague, Hitchcock ensured that the focus remained on the momentum of the narrative and the tension of the chase rather than the resolution of the mystery.31