Ancient Greek mythology tells of the wedding of the hero
Peleus and the water-nymph
Thetis, (they would become the parents of
Achilles). All the Gods and Goddesses were invited except for Eris - Goddess of Discord.
Eris was (understandably) slighted and as revenge stole one of the Wedding gifts, one of Hera's golden apples, and inscribed it with "For the fairest" (some texts say that it said "Property of the fairest"). Eris then threw it into the middle of the wedding party. The three proudest and most powerful Goddesses claimed the apple;
Hera,
Aphrodite and
Athena.
Zeus was called on to settle the dispute. He passed the buck onto
Prince Paris.
Hermes escorted the Goddesses to meet Paris at
Mount Ida, near
Troy.
Paris was unable to decide the case on its merits and opened the floor to bids. Hera promised Paris rule over Asia, Athena promised military glory, and Aphrodite offered him the most beautiful mortal woman. Paris ruled in Aphrodite's favour. Paris' new wife was the Greek Queen Helen of Sparta, who was already espoused to King Menelaus. Paris returned to Troy with his wife and the Trojan War began - with more discord than anyone except Eris herself could've imagined.
Thus, an 'apple of discord' no signifies a prize not worth the commotion it causes. The phrase morphed over time into "apple of commotion" and "apple of contention" - which were in common usage in the 17th century. By the 19th century the phrase had morphed again into "bone of contention".