What is the origin of the idiom "day in, day out" and when to use it?

The origin of the idiom "day in, day out" can be traced back to the natural rhythm of daily life. It draws upon the repetitive nature of everyday activities that occur on a daily basis. The phrase can be used in personal contexts to refer to the repetitive nature of one's daily life, such as work responsibilities, household chores, or personal rituals.