Screw your courage
I'm Lady Macbeth. I'm a strong, powerful woman. I know what I want and I'm not afraid to go after it. And you know what I think?
We fail!
But screw your courage to the sticking-place,
And we'll not fail. When Duncan is asleep--
Whereto the rather shall his day's hard journey
Soundly invite him--his two chamberlains
Will I with wine and wassail so convince
That memory, the warder of the brain,
Shall be a fume, and the receipt of reason
A limbeck only: when in swinish sleep
Their drenched natures lie as in a death,
What cannot you and I perform upon
The unguarded Duncan? what not put upon
His spongy officers, who shall bear the guilt
Of our great quell? (1.7.59-72)
Who Said It and Where
Macbeth wants to be king. The only thing standing in his way is the current king. But that might not be a problem for Macbeth, who's got a bright (murderous) idea.
In this scene, he sits alone in his castle, contemplating the whacking of King Duncan. That's where it gets a little complicated. See, if it were simply a matter of killing the king and then moving on without consequences, life would be simple, and Macbeth would be sitting pretty atop the Scottish throne.
The problem is what happens after the coup—the whole, being-damned-to-hell-for-the-sin-of-murder thing. Macbeth is supposed to protect the king, not murder him. Plus, Duncan is a pretty good king (if not a bit "meek"), and heaven is bound to frown upon murdering such a decent fellow.
In then end, Macbeth decides that it's probably not a good idea to commit murder. He has no justifiable cause to kill the king and he admits that he's merely ambitious. Enter Lady Macbeth. She gives her husband a good tongue-lashing, questions his manhood, and urges him on by attacking his masculinity. Apparently, that's a strategy that never gets old.
When Macbeth says "we will proceed no further in this business," Lady Macbeth responds by asking, "Art thou afeard to be the same in thine own act of valor as thou art in desire?" (1.7.3-4). Translation: do you think you won't be able to murder the king as much as you want to? Are you too afraid to go through with it? Are you really that much of a wimp?
There's also a dig at Macbeth's sexual performance at work here. Lady Macbeth implies that Macbeth is afraid his performance of killing the king will be just as weak as his performance in the bedroom (his sexual "desire"). Awkward. Save your marriage troubles for couple's counseling, please.
Either way, Lady Macbeth insists her husband is acting like an impotent coward. Ouch. According to her, killing the king, like satisfying your wife, will confirm Macbeth's masculinity: "When you durst do it, then you were a man" (1.7.4).
If Macbeth can't keep his vow, she says, then he isn't a man. Macbeth is a little turned on by this show of strength, and he finally resolves to go through with the murder. Luckily, Lady Macbeth has already hatched a plan and fills him in on the deets.