This quote appears in Shakespeare's Hamlet, spoken by Hamlet himself in Act 4 Scene 4: 'We know what we are, but know not what we may be.' It reflects the play's themes of self-discovery, uncertainty about destiny, and the potential for transformation. O Henry wrote twist-ending short stories, Elliot (likely T.S. Eliot) was a modernist poet, and Shelley was a Romantic poet - none wrote this Elizabethan dramatic line.