Shakespeare, in his plays, creates many contentious characters, multi-faceted and complex. Macbeth would appear to be one of these due to the presence of a fatal flaw. In Macbeth, he is at first gallant and victorious to the point that Duncan, the King, rewards him handsomely. Macbeth unfortunately, sees this more as the fulfillment of a prophesy he has just heard on this "foul and fair a day."(I.iii.38)
A series of unfortunate coincidences coupled with Macbeth's belief in the prophesies and his weakness in the presence of Lady Macbeth, all contribute to his ultimate downfall. His "vaulting ambition" which Macbeth recognizes as being his only reason for killing Duncan, will ultimately undo him.
After having decided against killing Duncan, but then being bullied by Lady Macbeth into being "more the man" (I.vii.51), Macbeth is almost in a trance as the bell rings and "invites me"(II.i.62)Even after he has done it, Macbeth cannot return to any sense of normality as he realizes what he has done. His guilt and fears promote more irrational behavior as he cannot "with all Great Neptune's ocean wash this blood clean from my hands."(II.ii.60-61)
Macbeth becomes more dependent on the witches prophesies and less dependent on anything else as he seeks to get affirmation for his actions. The witches know "something wicked this way comes" (IV.i.45) and that they can therefore manipulate Macbeth. Macbeth sees the witches intervention as if it is ordained so that even when they make ridiculous claims that "Macbeth shall never vanquished be until..."(92) and "none of woman born shall harm Macbeth,"(80)he cannot look towards their own motivations for destroying him.
Again, Macbeth's fatal flaw, his inability to see beyond his ambition, causes his self-absorption and he cannot look outside himself. Even Lady Macbeth's death is not enough to stop him, only to depress him. In becoming a tragic hero, he resolves the conflict by stopping at nothing, even when he knows he has been fooled by the witches and will be killed by MacDuff. It would be the only honorable (ironically) thing to do; to fight to the death.