In act 1, scene 6, King Duncan arrives at Macbeth's castle and enthusiastically greets Lady Macbeth by referring to her as an "honored hostess." King Duncan proceeds to thank Lady Macbeth for entertaining him on such short notice, and she demonstrates her capacity for dissembling by acting like a gracious, hospitable hostess. Duncan then praises Macbeth's great love for him and refers to Lady Macbeth as a "Fair and noble hostess." King Duncan then takes Lady Macbeth's hand and displays his complete trust in her by allowing Lady Macbeth to lead him into Macbeth's castle.
King Duncan is completely unaware that Lady Macbeth is actually hostile, dangerous woman, who is carefully plotting his assassination. In the previous scene, Lady Macbeth commanded evil spirits to fill her with cruelty and enable her to act upon her violent thoughts, saying,
Come, you spirits
That tend on mortal thoughts, unsex me here,
And fill me from the crown to the toe top-full
Of direst cruelty. Make thick my blood . . .(1.5.30–34)
Lady Macbeth conceals her true intentions by graciously inviting King Duncan into Inverness, and he is completely unaware of her bloody plans to murder him. Duncan's positive comments about Lady Macbeth are entirely wrong, and the audience recognizes that he should be on guard at all times when he is around her. Duncan's inability to recognize Lady Macbeth's evil intentions, while the audience understands that she is a threat, is an example of dramatic irony.