Final answer:
The last line of 'Mezzo Cammin' includes a somber reference to regret as the poet reflects on the midpoint of his life and expresses remorse for the lost opportunities.
Step-by-step explanation:
The last line of 'Mezzo Cammin' includes a somewhat startling and somber reference to regret. In the poem, the poet reflects on the midpoint of his life and expresses regret for the lost opportunities and unfulfilled aspirations. The line 'And half my life is gone and I have let / The years slip from me and have not fulfilled' conveys a sense of remorse and missed chances.