apple of discord

I would like to explain the meaning and example of the following ( and my fav.) idiom:

apple of discord
Meaning: anything causing trouble, discord, or jealousy.
Example: The run of two sisters for a single post has become an apple of discord, they are even fighting now.

Origion:
According to Greek mythology, the goddess Eris inscribed "to the fairest" and tossed in the midst of the feast of the gods at the wedding of Peleus and Thetis, thus sparking a vanity-fueled dispute among Hera, Athena and Aphrodite that eventually led to the Trojan War.