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

The origin of this phrase can be traced back to the 14th century in England, where "thick" referred to dense woods or forests and "thin" referred to open or sparse land. In this context, traveling "through thick and thin" meant to navigate through the densely wooded areas as well as the more open terrain. Over time, the phrase evolved to refer to the ups and downs of life and the loyalty required to support each other through all circumstances. It has become a common expression used to describe the unwavering support and commitment in relationships, friendships, and other important connections.