Here's a breakdown:
Sam Witwicky's Fate:
* The Audience Knows: The audience, through previous films, knows that Sam is destined for a crucial role in the war between Autobots and Decepticons. We see Sam in the first film actively working with the Autobots, and in the second film, he's been targeted by the Decepticons. This builds anticipation for his continued involvement.
* Sam Believes: Sam, however, is unaware of his real importance. He desires a "normal" life and seeks to distance himself from the Transformers. He even graduates college and gets engaged, seemingly putting the Transformers behind him.
* Irony: The audience knows Sam's "normal" life is a facade and that he will be pulled back into the conflict. His desire to escape is ironic, as he is destined to play a critical role.
Sentinel Prime's Deception:
* The Audience Knows: The audience is gradually introduced to Sentinel Prime's deception through subtle clues and his growing paranoia. His desire for Earth's resources and his distrust of the Autobots hints at his true intentions.
* The Characters Believe: The characters, including Optimus Prime, initially trust Sentinel Prime. They see him as a savior and a leader who can unite the Autobots and humans.
* Irony: The audience is aware of Sentinel Prime's true nature and knows that he is manipulating Optimus and the others. The trust and hope the characters place in him are a stark contrast to the audience's understanding of his intentions.
Other Examples:
* The Deception of the Wreckers: The audience is aware that the Wreckers are a group of Autobots that have been corrupted and are now working with the Decepticons. The characters, however, believe them to be allies.
* The Presence of the "Fallen": The audience knows that the Fallen is still alive and is secretly manipulating events from beyond the grave. The characters are unaware of his presence and the danger he poses.
Overall: The dramatic irony in Transformers: Dark of the Moon adds layers of tension and suspense to the narrative. It allows the audience to experience the story on a different level, knowing information that the characters do not. This enhances the film's impact and leaves a lasting impression on the viewer.