Macbeth, due to the introduction and importance of the supernatural, is considered to be Shakespeare's 'darkest' work, implying that, in some instances, circumstances were beyond the control of any normal person.
We see Lady Macbeth's descent into madness - and her isolation from society - as her conscience and sense of guilt gradually takes its toll. At first, she throws herself into her 'role' of ensuring Macbeth's rise to power but his distance - as he becomes more driven by the witches prophesies, eats away at her confidence. The ultimate display of her total isolation is in her committing suicide - clearly there is nothing than indicates desperation and a feeling of complete detachment and withdrawal more than suicide.
It is interesting to note the stark contrast between the way Macbeth reaches his complete isolation from all things civilized and humane and Lady Macbeth's.
Having seen Macbeth's 'rise,' the impact of his 'fall' is all the more dramatic and tragic. He is the noble hero who defeated the enemy in the name of his king. He is honorable and good.
It is the decision that he makes that will decide the course of his life and thus whether the play becomes a tragedy (where the hero is defeated through a fatal flaw).
Macbeth then gets caught up in the witches prophesies and the potential to be king - almost too much to bear. The fact that he got this far - Thane of Cawdor- by honost and ethical means seems to escape him as he ponders the ONLY way to succeed.
by fair means or foul.
The audience is lulled into a false sense of security when Macbeth realises the error of judgement he almost made in killing Duncan.
We will proceed no further in this business.
Macbeth is at least 'real' and exhibits confilcts and feelings in the normal course. Unfortunately, with Lady Macbeth's encouragement, it does not take long for him to change his mind. He
demonstrates that once the line dividing good and evil has been crossed, it is quite easy to proceed deeper into evil.
He has blinded himself to any other interpretation. So now Macbeth's downfall is assured; we see his distance from his wife, his mistrust of his friends and their mistrust of him. Banquo realises that his 'friend' seems 'possessed' and the prophesies are coming true:
Thou hast it now: King, Cawdor, Glamis, all
By the end, with Lady Macbeth dead, the only thing Macbeth has left is the witches and he clings to this realization
I bear a charmed life which must not yield
To one of woman born
Each moment has become agonizing for him and life meaningless.
He has achieved his ambition of power and discovered that it was nothing. He has sold his soul to evil and has received nothing. He has lost power, home, and family, but he feels nothing.
...it is a tale
Told by an idiot, full of sound and fury,