While the witches appear to have great skill at prophesying, it's not certain whether their prophecies are preordained. If not, do they simply encourage Macbeth to become active in constructing his own fate? It is perhaps part of Macbeth’s character to shape his life according to the predictions – whereas Banquo does not. This might explain why the only prophecy not realized by the end of the play relates directly to Banquo and cannot be shaped by Macbeth (although Macbeth would also have little control over the “Great Birnam Wood” prediction).
What Macbeth lacks in decisiveness, Lady Macbeth makes up for in bloodthirsty lust for power and wealth. Swearing off her femininity at the beginning of the play, Lady Macbeth manipulates her husband powerfully to follow through with his plans to kill Duncan. After the act of regicide, it is Lady Macbeth who has the soundness of mind to plant the incriminating evidence on Duncan's guards. And yet, her firmness disintegrates gradually as the play progresses, leading to nightmares that haunt her and ultimately drive her to suicide. In this regard, Lady Macbeth appears to switch characters with Macbeth midway through the play. Although most famous for her cruelty and lines such as "unsex me here," the decline of Lady Macbeth is also of great interest and certainly a mysterious aspect of Macbeth .