This is a genius narrative choice. By removing the future queen from the palace, the writers allow her to grow up without the constraints of the Bone Rank system. She learns to trade, to fight, to read people, and to survive on her wits—skills that no princess in the palace would ever possess. Meanwhile, back in the capital, Mi-shil consolidates her power, slowly poisoning the mind of the remaining twin, Princess Cheonmyeong (Park Ye-jin), convincing her that she is weak and worthless.
The "twin abandoned at birth" plot is a dramatic invention. Historically, Queen Seondeok (reigned 632–647) was King Jinpyeong's eldest daughter, and she rose to power due to a lack of male heirs, not as a lost twin. the great queen seondeok ep 1