In Shakespeare's Macbeth, how does ambition ruin Macbeth?

In Shakespeare's Macbeth, Macbeth
himself tells the audience that his "vaulting ambition" is what pushes him forward—that
and the ambitions of his wife.

There is no question that
the witches' predictions strike a chord with Macbeth. The idea of being King appeals to
him, though there is a great deal that stands in his way—first there is Duncan, and then
Malcolm (the King's son) who Duncan names as his heir. Though he is the King's cousin,
Macbeth is not next in line for the
throne.

However, Macbeth wants to be King. Even when he
hesitates because Duncan has been so generous in rewarding him for his efforts on
Scotland's behalf on the battlefield, Macbeth allows his wife to shame him into pursuing
the King's murder. She calls him a coward, but he tells her to be quiet: no one is
braver than he is...

readability="7">

MACBETH:

Prithee,
peace!

I dare do all that may become a
man;

Who dares do more is none.
(I.v.50-52)

When she finally
convinces her husband to move forward with their plan, it is obvious he does not
want to do it. First, he has many good reasons
not to kill Duncan: he is Macbeth's King, his cousin, his friend,
and his house-guest. Macbeth is not a murderer by nature. He has killed on the battle
field, but not in cold blood. However, his ambition (as he noted) drives him on. Even
seeing a "ghostly dagger" hovering before him on his way to the murder does not stop
him.

We can see, however, how this terrible act (for which
the Elizabethan audience believed he would go to hell—for killing a
King) starts to change the noble man we met at the play's beginning. It's not
just that he kills his King, but he begins to lose a sense of who he is—he is petrified
to return the daggers to the scene of the crime:

readability="7">

MACBETH:

I'll
go no more:

I am afraid to think what I have
done;

Look on't again I dare not.
(II.ii.64-66)

This is at
first encouraging in that we sense the honorable man inside him is fighting against what
Macbeth has done. However, he notes that killing will probably get easier with
practice—unfortunately, he is right. When the King's body is discovered, Macbeth
pretends to lose his mind in his "grief" over Duncan's death by killing the guards who
could expose Macbeth as the killer. From there, it only gets easier. He arranges for
Banquo and his son Fleance to be murdered (though Fleance gets away); he also has
Macduff's wife, children and servants slaughtered because Macduff turns his back on
Macbeth and goes to Malcolm who is living in exile in
England.

Ultimately, this course he embarks on also leads
to Lady Macbeth's insanity when their actions become (ironically) too much for her to
bear. Macbeth's ambition costs him a friend in Duncan and Banquo.
He loses his sense of morality. He teeters on the edge of insanity. And he loses his
wife to suicide. At the end, the only thing he has left is his refusal to run away or
die a coward's death.

readability="18">

MACBETH:

I
will not yield,

To kiss the ground before young Malcolm's
feet,

And to be baited with the rabble's
curse.

… I will try the last. Before my
body

I throw my warlike shield! Lay on,
Macduff,

And damn'd be him that first cries, “Hold,
enough!” (V.viii.32-39)

With
everything else that ambition costs Macbeth, it ultimately also costs him his
life.