Macbeth

Lady Macbeth’s first appearance in the play is when she is shown reading the letter that her husband has written to her about meeting the witches:
Glamis thou art, and Cawdor and shalt be
What thou art promised.
Lady Macbeth however knows the disposition of her husband and she thus knows that if possible what he wants most highly he would want to achieve holily. She sneers at what she considers his weakness: “th’ milk of human kindness”. Lady Macbeth feels she must find valour in her tongue to persuade Macbeth to abandon those scripts which prevent him from seizing the crown.

Throughout the first act Lady Macbeth seems the stronger partner and she invokes supernatural powers and calls for “spirits” more powerful than her own:

... Come, you spirits
That tend on mortal thoughts, unsex me here,
And fill me from the crown to the top, top-full
Of direst cruelty...
At this point the audience is introduced to both Macbeth’s and Lady Macbeth’s ambition and determination. They understand each other very well even though neither one of them mentions murder. Lady Macbeth offers her husband advice and instructs him in the arts of hypocrisy while she herself takes on the role of managing events: “Look like th’ innocent flower, But be the serpent underneath”.

When Macbeth seems to doubt whether to “proceed no further in this business”, his wife, who has committed herself to the powers of darkness calls him a coward: 

... Art thou afeard
To be the same in thine own act and valour,
As thou art in desire?

She urges him to act by attacking his manhood and Macbeth replies:
I dare do all that may become a man
Who dares do more is none.
Lady Macbeth’s argument and scorn are overwhelming and she seals up her persuasion with a horrifyingly inhuman image of a woman who dashes out the brains of her suckling child to shame Macbeth into keeping his word to her.

This moves Macbeth and he voices his fear of failure. She sweeps aside his questions about failure and...