What is the origin of the idiom "bite the bullet" and when to use it?

The idiom "bite the bullet" has its origins in the practice of medicine during the 19th century. Before modern anesthesia, soldiers and patients would bite on a bullet or a similar object to endure the pain during surgery or other medical procedures. Figuratively, the idiom is used to describe the act of facing a difficult or unpleasant situation with courage and determination, even though it may be uncomfortable or painful.