What is the origin of the idiom "day and night" and when to use it?

The idiom "day and night" has its origin in Old English and has been in use for centuries. Its roots can be traced back to the Germanic language family, which includes Old English. The phrase evolved as a way to express the contrast between these two periods of time. As a result, "day and night" became a commonly used to express to describe the continuous passage of time and the uninterrupted nature of certain actions or conditions. It is often employed to describe intense or relentless efforts, often in relation to work, study, or dedication.