I keep rewatching it, and Kim Ji-soo's character is so heartbreaking and pitiful

Eun-ju…
Her sister Geum-ju (Yoon Hae-young), who is only a year older, received so much love from their mother.
She grew up spoiled like a princess and lived at her grandmother's house until she was six.
She wanted to study art, but because of their financial situation, she was forced to go to nursing school.
Even when she gets a job and gives money to her mother, her mother just takes it for granted.
Even after they became sisters-in-law through a double marriage, her mother only looks out for Geum-ju…