He seems To have seen better days, as who has not Who has seen yesterday?

The speaker wryly undercuts the commonplace remark that someone “has seen better days.” Byron turns it into a universal condition: anyone who has lived long enough to have a “yesterday” has already accumulated loss, disappointment, or nostalgia. The line’s epigrammatic twist suggests that decline is not exceptional but built into time itself—experience inevitably makes the present feel diminished beside remembered moments. The humor is bleak rather than light: it acknowledges how memory edits the past into “better days,” while the mere passage of time ensures that every new day can be measured against what is gone.