Macduff's mission to Malcolm finally reaches its dramatic conclusion in the fight with Macbeth, where Macduff makes a shocking revelation of his own in relation to the status of his own birth - so much so that what he says almost pulls the ground from under Macbeth's feet and almost floors him before any fight. As he squares up to Macduff, Macbeth taunts his adversary with the threat that no man born on earth can ever kill him. Then Macduff tells him about his own Caesarean birth. Taken aback, Macbeth then refuses to fight and Macduff is about to accomplish his mission to get rid of his opponent and Macbeth stares into the face of his final disaster. His 'charme'd life' has ebbed away and he is down on his luck so Macduff's mission as a 'coup' is complete as he tells Macbeth he will be an exile and always a prisoner.The idea of luck running out has lasted to this day in this particular play with stories of riots and deaths attached to its performance. Many actors won't even say it's name.
Concerned about Macbeth's tyrannical reign as king of Scotland, Macduff goes to England to seek Malcolm's assistance in overthrowing Macbeth. Malcolm is the rightful king because King Duncan, before he was murdered, named his son the Prince of Cumberland, indicating his wish that his son serve as king after him. Macduff hopes to convince Malcolm of Macbeth's tyranny as king by telling him of the way that Scotland is suffering under his rule:
Each new morn
New widows howl, new orphans cry, new sorrows
Strike heaven on the face... (4.4.5-7).
Macduff, however, must first prove to Malcolm that he himself is not treacherous or some kind of spy sent by Macbeth; also, the prince tests Macduff's loyalty to Scotland by insisting that he has only wicked traits, no redeeming ones, and would not be a suitable king for Scotland. When he asks Macduff if he thinks Malcolm would be "fit to govern," Macduff in despair replies, "No, not fit to live." He almost gives up his mission until Malcolm reveals that he was testing Macduff.