We usually think that feeling guilty is pretty unproductive, but watching the Frog and Peach Theatre Company's Macbeth on the tail of Hamlet suggests that guilt propelled Shakespeare to pen some of his most famous lines.
Hamlet and Macbeth are plagued by guilt even when only considering acting badly, and while Queen Gertrude and Lady Macbeth come to guilt more slowly, some of their most famous speeches are born from their apprehension of such personal reckonings. Guilt comes to these characters as visual hallucinations--the "dagger of the mind," the ghost of Hamlet's father, Lady Macbeth's bloody hands--partly because theater is a visual art and we must be made to see the guilt rather than only hear of it. Yet it is the guilt which makes them human, evoking that pity which Aristotle deemed essential to good (and socially beneficial) tragedy, so while Hamlet and Macbeth have certainly "supped full of horrors" in ways most of us can never imagine, their mental torments are familiar to us. After Macbeth slays Duncan, he comes wretched to Lady Macbeth asking "Wherefore could I not pronounce 'Amen'?" Certainly we all might recognize and take caution from our failures to speak the right words at the right time. When Duncan tells a soldier: "So well thy words become thee as thy wounds," we might likewise wish to be thus applauded.