In Act Three, scene two of Shakespeare's Macbeth, Macbeth and Lady Macbeth are both unhappy.
Lady Macbeth is displeased because she and her husband have invested everything—their mortal souls even—in killing Duncan, but still they cannot enjoy that which has come at such a "high" price. The biggest reason that they cannot enjoy ruling Scotland as King and Queen is that Macbeth is so worried over everything—even though she feels he should be past that. Lady Macbeth tells Macbeth not to be concerned: why should he worry about the murder of Duncan when Duncan is dead?
How now, my lord! Why do you keep alone,
Of sorriest fancies your companions making,
Using those thoughts which should indeed have died
With them they think on? Things without all remedy
Should be without regard. What's done is done. (III.ii.10-14)
Macbeth explains that while they have killed Duncan, they are not guaranteed the throne. He says:
We have scotch'd the snake, not kill'd it. (line 15)
He means that while Duncan is dead, there are other threats to them. He specifically points out Banquo. It eats at his mind that he has bartered his soul to the Devil by killing the King (a mortal sin in the eyes of Elizabethans), only to have to worry about the witches' prediction regarding Banquo fathering a line of kings. In his anguish he cries out to Lady Macbeth:
O, full of scorpions is my mind, dear wife!
Thou know'st that Banquo and his Fleance lives. (lines 40-41)
Lady Macbeth reminds him that neither of them will live forever— Banquo and Fleance will eventually die. Macbeth calms himself with this idea, and—ironically—tells his wife to pay a lot of attention to Banquo at the feast they are planning that night. It is ironic in that Macbeth already has a plan in place to kill Banquo and Fleance, and he knows then that Banquo will never make it to the feast. And while he lets Lady Macbeth know that he has made some "arrangements," for the first time Macbeth chooses not to share the specifics with his wife: a subtle sign that they are growing apart.
Instead, Macbeth tells his wife to wait until the deed (whatever it is) is done and then she should congratulate him.
Be innocent of the knowledge, dearest chuck,
Till thou applaud the deed. (lines 50-51)
At this point of the play, Lady Macbeth is unhappy that they cannot relax and enjoy what they have (an echo of what Macbeth said to her when he suggested they wait to kill Duncan in Act One, scene seven). Macbeth, on the other hand, is becoming paranoid, seeing threats all around him. And while he insanely sees Fleance (a young boy) as an impediment to keeping his crown, Macbeth is accurate to worry about Banquo—for Banquo has already told him that he will not compromise his ethics for anyone.