Lady Macbeth’s speech beginning ‘We fail! But screw your courage to the sticking-place, and we’ll not fail’ comes at the end of Act 1 of William Shakespeare’s Macbeth. Lady Macbeth’s words come just after she has taunted her husband for his perceived lack of manliness, because he is now vacillating and having second thoughts about their plan to kill Duncan so Macbeth can seize the crown of Scotland for himself. We have analysed the earlier exchange between Macbeth and Lady Macbeth here.
Let’s take a closer look at the ‘screw your courage to the sticking-place’ speech, offering a summary and analysis of its meaning and language as we go.
LADY MACBETH:
We fail!
Even before we get to the famous line about screwing your courage to the sticking-place, we have these curious two words from Lady Macbeth, which, like another short statement from the play (Macduff’s ‘He hasn’t any children’) can be interpreted in three very different ways.
Indeed, as Kenneth Muir observes in the notes to the excellent Arden edition of the play, “Macbeth” (Arden Shakespeare: Second Series), the eighteenth-century actress Mrs Siddons variously rendered the line as ‘We fail?’ (i.e., ‘how could we fail when the task ahead is so easy?’), as ‘We fail!’ (as in ‘how could the two of us, given how cunning and strong we are, possibly fail? Others might, but we cannot, don’t be stupid!’), and, finally, as ‘We fail’ (i.e., not a question, nor an exclamation of incredulity, but a simple statement: ‘so, if we fail, we fail: so be it’).
Of course, these three renderings all give Lady Macbeth’s two words a very different meaning. But as Muir notes, critics have argued in favour of all three, so it’s impossible to say which Shakespeare intended. However, the First Folio (the first time the play was printed) has a question mark, so ‘We fail?’, which, although published after Shakespeare’s death, was assembled by actors who worked with Shakespeare.
But screw your courage to the sticking-place,
And we’ll not fail.
If Macbeth can recover his courage, they will not fail. ‘But screw’ means ‘Only screw’: in other words, all Macbeth requires is a little courage now. Muir once again alerts us to the multiple meanings of the image conjured by ‘screw your courage to the sticking-place’, which is interpreted variously as referring to the screwing up of strings on a viol (stringed instrument) and a soldier screwing up the cord of his cross-bow to its ‘sticking-place’, ready to shoot a quarrel or bolt.
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
Lady Macbeth outlines her plan: when Duncan is asleep (and his journey to the Macbeths’ castle will have tired him out) she will get his two ‘chamberlains’ (or servants, gentlemen-of-the-bedchamber) drunk with wine and ‘wassail’ (a spiced mulled cider usually drunk during the cold months of the year).
That memory, the warder of the brain,
Shall be a fume, and the receipt of reason
A limbeck only:
These chamberlains will be so drunk that they will not be able to remember what happened. Memory was regarded in Shakespeare’s time as at the back of the brain, and so was regarded as the ‘warder’ of the cerebellum in that it kept watch over the rest; but in Shakespeare’s image, memory is transformed through drunkenness into a fume or haze, which clouds the rest of the brain. Thus the brain becomes like an ‘alembic’ or ‘limbeck’, the cap part of distilling apparatus.
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?
When these servants lie asleep like pigs, dead to the world, Lady Macbeth and Macbeth will be able to do whatever they want to Duncan, unguarded as he will be. And they can put all the blame upon the chamberlains (‘spongy’ being a rather delightful synonym for ‘drunken’ here; ‘quell’ refers to Duncan’s murder, a word that shares the same root as the word ‘kill’).
MACBETH:
Bring forth men-children only;
For thy undaunted mettle should compose
Nothing but males. Will it not be received,
When we have mark’d with blood those sleepy two
Of his own chamber and used their very daggers,
That they have done’t?
‘How many children had Lady Macbeth?’ was the title of a long essay by the critic L. C. Knights, published in 1933, mocking the school of criticism (ultimately influenced by the critic A. C. Bradley) which seeks to ask, and answer, such 
questions about details hinted at, but not confirmed, in the play concerning characters’ lives. Clearly Lady Macbeth has had children (and ‘given suck’, as she had put it in her earlier speech in this scene), but she and Macbeth appear to have no living children; at least, they’re never mentioned.
Here, Macbeth tells his wife to give birth only to male children, for her fearless spirit or ‘mettle’ could create nothing but masculine children. He then returns to the plan, asking her if she truly believes people will accept the chamberlains’ guilt as true, if the Macbeths make it look as if those hapless servants are the guilty ones.
Note how quickly Macbeth has been converted to his wife’s scheme (as Muir points out): as soon as she offers a practical way forward, he is sold on it. It’s also worth noting the vulnerability of his questioning here (‘Will it not be received …’): he is clearly easily led by his smart and quick-thinking, pragmatic wife.
LADY MACBETH:
Who dares receive it other,
As we shall make our griefs and clamour roar
Upon his death?
In other words, ‘who would dare believe otherwise, when you and I, dear husband, will make a big show of being distraught and angered by Duncan’s death?’ Note: ‘griefs and clamour’ might be analysed as an instance of hendiadys, a rare but fascinating rhetorical device whereby two closely related things are joined oddly by an ‘and’: so ‘griefs’ and ‘clamour’ should not be viewed as two separate things, but as wholly associated, so ‘griefs and clamour’ really means ‘clamorous griefs’.
MACBETH:
I am settled, and bend up
Each corporal agent to this terrible feat.
Away, and mock the time with fairest show:
False face must hide what the false heart doth know.
The scene – and the act – ends with Macbeth telling his wife that he is happy with the plan she has outlined, and every part of his body will now be given over to carrying it out. He tells his wife to leave him, and put on a good show in front of their guests, to delude them into thinking nothing suspicious is going. Her lying face must hide what her lying heart knows is about to take place …