William Shakespeare's tragic play's (Macbeth) protagonist (Macbeth) possesses harmatia. According to the characteristics of the tragic play (as defined initially by Aristotle's Poetics), the tragic hero must possess harmatia (which is Latin for tragic flaw). In the case of Macbeth, his tragic flaw is that of his growing ambition.
After hearing about the prophecy of Macbeth's rise to the throne, from the witches, Macbeth initially decides to leave his fate to chance (meaning he will not act upon the prophecy in order to gain the throne himself).
If chance will have me king, why, chance may crown
Without my stir.
This statement, made in Act I, scene iii, is Macbeth's initial reaction. Later, after telling his wife about the prophecies, the pressure she places upon him is overwhelming. Believing that her husband is not capable of what needs to be done (for hi to gain the throne), Lady Macbeth belittles him.
Yet do I fear thy nature;
It is too full o’ the milk of human kindness
To catch the nearest way. Thou wouldst be great;
Art not without ambition, but without
The illness should attend it.
Lady Macbeth's questioning of Macbeth's manhood and his ambition proves to Macbeth that he must make some changes in his life. Macbeth agrees to murder Duncan.
After the murder of Duncan, Macbeth's worries do not go away. Banquo knows about the prophecies (and how his own sons shall be kings). Not only that, many of Macbeth's followers question his coming to the throne and his ability to be a good king.
In order to keep the throne, Macbeth has both Banquo and Macduff's family murdered. His ambitious nature has become too much for him to handle.
Essentially, without his ambition, Macbeth would have come to the throne when "chance" deemed it appropriate. His ambition led him down a path of destruction, ending in his own murder.