Who is responsible for Macbeth's demise in Macbeth?

Although many
factors contribute to 's imminent downfall, the play suggests thatalone is to blame for his own
demise. He admits that his own ambition is the very reason he cannot prevent himself from
committing evil deeds:

Stars, hide your
fires;
Let not light see my black and deep desires...

I have no
spur
To prick the sides of my intent, but only
Vaulting ambition, which
o'erleaps itself