He was without moral compass; devoid of original thought; and highly ambitious.
She shared the first and last: with the addition of cunning and ability to commit to purpose.
He supplied the opportunity; she the means of support to make the fatal choice.
They were Machiavellian by nature: two people creating misery for their own end.
Verdi's Macbeth entices you into the tale with the same questions, regarding fate versus free will, found in Shakespeare's play. His opera portrays the characters as emotionally human...people who are caught up in their own drama and who are creating their own tragedy, and revealing it. You cannot escape your own fate. What that fate is depends on choice.
Are the witches who predict Macbeth to become King of Scotland, the vespers in his head; egging him on in the delusion that he is special and standing outside of moral norms? He has been conferred with honours in reality. They prove not to be enough.
Does his need to be special coincide with hers, or is she simply heartened by greed?
In the end they are corrupted by their ambitions, go mad (in the sense that they are not right in the head) because they have done evil (in a truly epic sense) and die: remembered for the monsters that they were.
There is a reason this tale lives on.
Note: since it was first produced (around 1606) the play was rumoured to be cursed. There are many stories throughout the years of mishaps, but suffice it to say that to utter the name of this play in a theatre is considered to be bad luck. Thus, this tragedy is known as the Scottish Play or the Bard's Play etc.