Macbeth is ultimately responsible for killing Duncan, but Lady Macbeth and the Weird Sisters bear some moral responsibility for encouraging and assisting him in the commission of his crime.
Lady Macbeth claims that she herself would've carried out this wicked act herself if Duncan hadn't resembled her own father as he slept. But we must take this with a large pinch of salt. It's almost certain that Lady Macbeth wouldn't have plunged in the dagger herself, whatever the circumstances. Though she may have actively planned the whole thing, it was always understood that it was Macbeth who'd have to wield the knife. Nevertheless, Lady Macbeth is fully complicit in this heinous act of villainy, and she must share some of the blame for what's happened.
As indeed must the Weird Sisters. It was they who planted the demon seed of ambition in Macbeth's mind. They were the ones who encouraged Macbeth to take the fateful step of making himself king of Scotland, irrespective of the methods used to achieve...
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