A major theme in "Julius Caesar" is public self versus private self, explains SparkNotes. Brutus and Caesar each struggle with this internal conflict and their choices drive much of the play's action.
Brutus sets aside his personal friendship with Caesar and goes along with the plot to murder him, believing he is acting out the will of the people. Brutus does not see Caesar as his friend, only as a man with too much power. Similarly, it is Caesar's neglect of private concerns in favor of his public self that leads to his death. Calpurnia, who dreamt of Caesar's murder, begs him to stay home and he agrees until he learns the senate wishes to give him the crown. It is this internal struggle that has led critics to praise the play for refusing to categorize the characters as either heroes or villains, states SparkNotes.