In Macbeth, having just murdered Duncan, Macbeth is already questioning himself, realizing that, as he says, "'twere best not know myself,"(II.ii72). However, at the beginning of Act II, scene iii, he changes quickly from the doubting, confused and possibly remorseful Macbeth, to a calculating murderer, determined to carry through the plan. His references to "a rough night," (II.iii.59) mean far more to Macbeth and to the audience than the words themselves. Having been rewarded with a title because of his valor, he is now scheming and covering his tracks by admitting to having killed Duncan's guards, suggesting that he did so out of loyalty and love for his king, when he saw that Duncan was dead. He is notably more bold and already seems less reliant on Lady Macbeth.
With his new-found confidence, Macbeth has arranged to have Banquo killed because, as he says, "Under him, my Genius is rebuked," (III,i.55) which means that Macbeth sees Banquo as a threat to Macbeth's own future as king. However, in Act III, scene iv, Macbeth learns that, although Banquo is dead, his son, Fleance escaped and he says that he feels, "Cabin'd, cribb'd confin'd," (III.iv.24). He is so affected by this news that he imagines the ghost of Banquo and it is necessary for Lady Macbeth to step in and suggest that he is having a "momentary" fit as his behavior is sure to expose what they have done otherwise. The fact that it is Lady Macbeth who calms Macbeth reveals the change in Macbeth as he, once again, relies on her steadfastness and undaunted personality to move their plan forward. His fearlessness is replaced by fear and now he feels that he also needs to meet with the witches as he is questioning his future. It is clear to the audience that he is delusional because, with Lady Macbeth's support and having made his decision to visit the witches again, Macbeth convinces himself that, "We are yet but young in deed," (143), and therefore there is a chance that this whole problem will resolve itself.
By the time we see Macbeth in Act V, scene v, he, yet again, feels invincible because, having met with the witches, he is convinced that he cannot be beaten. Based on the apparitions which confirmed that, "None of woman born,"(IV.i.80) can defeat him until the wood "Shall come against him,"(91), Macbeth, in Act V, scene v admits that he has, "Almost forgot the taste of fears," (9), suggesting that nothing scares or alarms him. He is saddened by the news that Lady Macbeth is dead and the change here, when the messenger alerts Macbeth that the wood seems to be approaching, such as was described by the witches, is Macbeth's acknowledgement that the witches were possibly lying. As he says, he is beginning "to doubt the equivocation of the fiend," (43) the witches being representative of the "fiend." He is however, ready to die, "with harness on our back," (52), suggesting that he believes that he still has some degree of honor.