William Shakespeare's Macbeth is a play outlining the fall of the tragic hero. Macbeth's downfall was not caused by any single cause, but by many underlying causes working in unison. The influence of Lady Macbeth, the Weird Sisters, and even Macbeth himself lead to his downfall. Primarily, Macbeth's own ambition and deceit serves as the downfall as slowly the shift is made in which the evil influences, which were predominately external, begin to shift to the internal workings of Macbeth himself.
At the beginning of the play, the Weird Sisters are preparing to meet with Macbeth, and the important imagery of "Fair is foul, and foul is fair," is first introduced. Throughout the play, the idea of things being other than they seem arises time and again. Soon thereafter, Macbeth himself says "So fair and foul a day I have not seen," implying the witches influence over him. The prophecies of the witches play an important role in this play. The witches prophesies that Macbeth will be Thane of Cawdor and eventually King. Upon hearing this, Macbeths starts, and Banquo replies to this "Good sir, why do you start and seem to fear // Things that do sound so fair?" This is perhaps the moment in which Macbeth realizes his potential and his ambition takes over. When Macbeth learns that he is, indeed, the Thane of Cawdor, he begins to heed the witches words as being "fate." This, in turn, drives Macbeth to actions he wouldn't normally endeavor to do in the name of "fate," when rather !.
it is his own deeds that drives the forces about him. Though Banquo warns him about giving any faith into the witches words, Macbeth chooses to anyway.
Lady Macbeth is but another evil external influence on Macbeth. When she hears of the prophesy, and of Macbeth's new title, she herself becomes obsessed with the idea of Macbeth as King (and subsequently herself as queen). The Lady devises a plan to murder Duncan to try to assure Macbeth the crown.