Macbeth faces a dissonance when he murders Duncan. He knows that murdering the king is wrong, yet he convinces himself (with some persuasion by Lady Macbeth) that going through with the murder is the only way that he will become king. The disconnect between Macbeth's morals and his actions cause him to feel extreme guilt immediately following the murder. Macbeth again faces dissonance when he tells all the thanes to "fly" once he learns that many of them have left his side to fight for the English army. Macbeth does not want to be abandoned and he wants the love of his men, but his actions are proud and do not reveal his inner thoughts. Finally, Macbeth falsely assumes that no one can hurt him because he misinterprets the witches' prophecy. The witches tell him that he needs to use caution--especially around Macduff, but Macbeth disregards all caution when entering into combat with Macduff at the end of the play.
In the field of psychology, cognitive dissonance is a term used to describe the mental state of a person attempting to hold on to two contradictory beliefs. This causes an emotional tension that can only be resolved by abandoning one of the two beliefs. In the case of Macbeth, he has a set of moral values which contradict his belief that he needs to do certain things in order to achieve his ambitions. Over the course of the play we gradually see him abandon many of his values to pursue his ambitions. Three examples of this are:
- Listening to the witches: As Macbeth is a Christian and witchcraft was believed to be the work of the devil, listening to the witches and taking their advice contradicts his system of religious beliefs.
- Killing Duncan: Not only is murder forbidden in the Christian religion, but also loyalty to one's king was an important civic virtue.
- Banquo's death: Having Banquo killed not only violates a system of belief that condemns murder but also breaks the bonds of friendship. In order to do this, Macbeth needs to gradually abandon a belief in community and fellowship in order to become a solitary despot.