Two such opposed kings encamp them still
In man as well as herbs, grace and rude will;
And where the worser is predominant,
Full soon the canker death eats up that plant.
– William Shakespeare
Romeo and Juliet, Act 2, Scene 3. Friar Laurence says that the dual nature of poison and medicine found in herbs, is also present in people. People have two sides to their nature, one evil and the other good. A metaphor compares this duality to "opposed kings." The friar also warns that where the evil side is stronger that becomes a cancer that kills. This is foreshadowing of how Romeo and Juliet, though they love each other, will be destroyed by the hatred surrounding them.