Answer:
Lady Macbeth's ambition to see her husband become King
Explanation:
After Macbeth's meeting with the three witches, he went ahead and told his wife of the revelations. Now, Macbeth wanted to rule, but left to him he wouldn't have committed the gruesome crime i.e murdering Duncan in cold blood. However, Lady Macbeth is not of the same sensibilities with her husband and would do anything to make him a King.
She pestered him incessantly and struck at his ego, he's being a coward for not doing what the witches had foretold. She manipulated Macbeth into killing Duncan and she implicated the innocent guards.
After this gruesome murder of an innocent man, neither Macbeth nor his wife know peace and the actions of that night ruined them all.
