What does the line "fair is foul, and foul is fair" mean in Shakespeare's play Macbeth?

"Fair
is foul and foul is fair," first uttered byin Act 1, Scene 1, is athat sets the stage for
the entire play.  At its most basic,  it means that "good is bad and bad is good."  In
the context of the play itself, it means that things that are good are also bad and vice-versa.
 For example: 's murder of Kingis good for , as it leads him to become the kind of Scotland, but
bad for King Duncan.  To continue to explore this particular example: Macbeth's reign is
initially good for him and , but bad for the country.  In Act 4, Scene 3,