Drama's vitalest expression
Common Day
Dickinson capitalizes 'Common Day' like a character name—ordinary life gets the same typographical dignity as 'Hamlet.' She's already arguing her thesis in the formatting.
boxes shut
Theater boxes are the private seating areas for wealthy patrons. When the performance ends, these literal boxes close—but the metaphorical boxes of the heart stay open.
to himself
Without Shakespeare's play, Hamlet would still exist—just as a private person experiencing his own dilemmas. The tragedy would be real but unrecorded.
leave no second
'Leave no second' means 'leave no copy' or 'leave no duplicate.' Romeo's love for Juliet is unique, unrepeatable—yet Dickinson argues every real love story is equally unrepeatable.
Owner cannot shut
The 'Owner' is the person living the drama—you can't close your own heart the way a theater owner locks the doors. Private tragedy runs continuously.