Irony

• Duncan comments (1:2) that he will no longer be deceived by the Thane of Cawdor by putting him to death when he attempted to take the throne. Ironically, the new Thane of Cawdor, Macbeth, tries (and succeeds) to do the same thing.
• Duncan comments that some people may appear good and trustworthy but may not be. He seems to have a good understanding of people yet misjudges Macbeth (1:4).
• Duncan feels the "castle hath a pleasant seat", judging the castle to be welcoming, which is ironic as it's where he will be killed (1:6).