What is the origin of the idiom "through the mill" and when to use it?

The idiom "through the mill" has its origins in the milling industry, where grains are ground between heavy stones or rollers to produce flour. The process of milling involves subjecting the grains to intense pressure, grinding, and refining. Figuratively, the idiom means to undergo a difficult, challenging, or rigorous experience that tests one's resilience, character, or endurance. It implies enduring a series of hardships, obstacles, or trials that can shape or refine a person.