What is the origin of the idiom "behind the eight ball" and when to use it?

The idiom "behind the eight ball" has its roots in billiards or pool, where being behind the eight ball is a challenging position, as it limits the player's options for their next shot. In a figurative sense, it is used to describe a situation where someone is in a difficult or unfavorable position, often due to past actions or circumstances, and faces an uphill struggle to improve their situation.