In "MacBeth", the witches' contradictory prediction of "fair is foul, and foul is fair” is an ongoing motif in the play that explains that appearances can be deceiving. At first glance, Macbeth finds the witches to be hideous, but he thinks that their predictions are appealing. Also, things that are good become bad, and things that are bad become good. This refers to the prediction of Macbeth to become king (which was supposed to be a good thing) but quickly turns sour when he betrays Duncan to take the throne.
This contradiction proves to be true in act one, because of the way that Macbeth and Lady Macbeth act versus the way they appear to be. They put on faces and pretend that they are welcoming hosts to Duncan, all while they are planning his murder. They are foul inside, but being fair on the outside.
