Macbeth's straight mind was short lived, as soon as his wife spoke her words of cruel persuasion . . . "Is this a dagger which I see before me, the handle toward my hand? Come, let me clutch thee! I have thee not, and yet I see thee still. Art thou not, fatal vision, sensible to feeling as to sight? Or art thou but a dagger of the mind, a false creation, proceeding from the heat-oppressed brain?" (Act 2 scene 1, lines 41-47). In this it is evident just how unstable Macbeth is becoming after the demands of his wife to murder King Duncan. Hallucinating a dagger before actually drawing his own shows the internal battle Macbeth is waging with himself to perform the treacherous task.
Macbeth isn't the only one who can't keep his mind on the path of the "straight and narrow", Lady Macbeth begins to feel the pressure as well. While Macbeth is performing the unlawful death Lady Macbeth becomes very panicky "Alack, I am afraid they have awaked, and 'tis not done. Th' attempt and not the deed confounds us. Hark! I laid their daggers ready; he could not miss 'em. Had he not resembled my father as he slept, I had done 't." (Act 2 scene 2, lines 11-15). This proves the lack of faith that Lady Macbeth has in her husband, and also the absences of her once-so-evident control over the situation. Later after the King is dead and Macbeth is crowned Banquo becomes very suspicious, and, Macbeth knowledgeable of Banquo's suspicions. No matter how false a face Macbeth wears nothing can hide his paranoid thoughts, he says to himself, "To be thus is nothing, but to be safely thus. Our fears in Banquo stick deep, and in his royalty of nature reigns that which would be feared. 'Tis much he dares; and, to that dauntless temper of his mind, he hath a wisdom that doth guide his valor to act in safety. There is none but he whose being I do fear; and under him, my genius is rebuked.