。
There's always tomorrow.
Literal
Tomorrow [quotative-と] say day [also-も] exist.
A proverb-adjacent phrasing using the 'day called X' construction. The も here is the softer 'also/too,' implying 'today isn't the only day — there's tomorrow too.' A comforting, encouraging sentiment that often appears alongside its grimmer counterpart 明日という日は来ない. Japanese frequently relies on particle nuance to shift philosophical tone.