William Blake's poem “A Poison Tree” with its extended metaphor of the tree that grows from wrath and bears a poisoned apple could be read as a plot summary for Shakespeare's Romeo and Juliet. Let's see how that works.

Blake's poem reflects on the nature of a grudge. If a person is angry with a friend and says so, then the issue can be dealt with and put aside. But foes do not discuss their grievances calmly and rationally, and those grievances then grow. To paraphrase the poem, they are watered by fears and tears, sunned by fake smiles and deceit. Eventually the anger grows into a poisoned apple that kills the foe who is trying to steal it from the tree. In other words, anger and feuds kill.

This is exactly what we see in Romeo and Juliet. The Montagues and Capulets have been feuding for years. They refuse to discuss their grievances. Instead, they nurture their anger through continued violence, so much so that Prince Escalus threatens to execute the next person who disturbs the peace with this feud. But the prince's threat does not stop the violence and the secret wedding of Romeo and Juliet. The poison tree, so to speak, keeps on growing as the two families fight in the street. And this anger grows a poisoned “apple” leads to the suicides of Romeo and Juliet (Romeo even kills himself by drinking poison). Each family then sees both a foe outstretched beneath the metaphoric poison tree and a beloved child.