What is the origin of the idiom "apple of discord" and when to use it?

The idiom "apple of discord" refers to a source of conflict or discord that arises from a seemingly innocent or insignificant issue. The origin of this idiom can be traced back to Greek mythology. According to the myth, Eris, the goddess of discord, threw a golden apple into a gathering of gods and goddesses with a label that read "for the fairest." This act sparked a dispute among the goddesses Hera, Athena, and Aphrodite, leading to the events that eventually led to the Trojan War. This expression is used to describe a specific issue or topic that becomes a significant source of conflict or disagreement among individuals or groups.