From what we see of the wealthy characters, their careers and status reflect who they are as a person.
Yeo-jeong works as a doctor, a career that involves working with a variety of people to help them with their care and health. Having extensive knowledge to human body means that they can also have the ability to kill as well. He is Dong-eun's solid ally throughout her revenge scheme and will not hesitate to dirty his hands to help her achieve it.
Jae-joon is an heir to a country club and owns a shop, which is accessible exclusively to wealthy people.
Yeon-jin is the wife of a business man and a weather caster, emphasizing her power status and having all the attention on her.
Sa-ra is an artist and the daughter of a church pastor, keeping up the appearance (like a painting) that she’s a saint (when she’s in fact a sinner). Plus, there have been reveals about how corrupt churches can be (like the Catholic Church covering up molestations of boys). And she’s as corrupt as the Catholic Church.
Do-yeon is a CEO of a construction company, which focuses on demolition and creation of buildings. But what causes buildings to become unstable? A lack of strong foundation. In other words, his household/family lacks a strong foundation (coming from the lack of loyalty from Yeon-jin and the reveal that his daughter isn’t his biologically).
Why did the school nurse leave instead of staying at the school? She wanted to take a third option. She was given two choices: either continue working at the school but pretend Dong-eun isn’t having problems, or lose her job and potentially get blacklisted from other job. If she did the former, she’d have to carry the guilt of not stepping in when she was supposed to. The latter would make it hard for her career wise and she needs to work to make a decent living. So what’s the third option she took: she resigned on her own accord. With this option, she was able to find financial stability, and was able to find another way to help Dong-eun out without compromising both of their well-being.
Dong-Eun is frequently seen eating kimbap, even though she passes out at one point due to malnutrition. It makes sense after she has a panic attack after hearing and smelling a barbecue grill since it reminds her of when she got her burn scars. Kimbap is light, portable and can be eaten cold, so not only is it suitable for eating during a stakeout, but she also won't risk having another panic attack by eating something that requires her to cook and use heat-based appliances.
Why does Dong-eun continue communicating and even forgiving the nurse despite leaving, but cuts ties and wants nothing to do with her former friend Kyung-ran? Well, actions speak louder than words. Kyung-ran knew Dong-eun was being bullied but did nothing, even going as far as ignoring her in school. The nurse tried to help Dong-eun but was forced to leave, with the latter knowing that the nurse's hands are tied. Despite leaving, she continued to help Dong-eun regardless.
Yeon-Jin is told by her mother as a teenager that, according to the shaman her mother attends, Yeon-Jin needs to avoid people with ieung (the korean letter ㅇ) in their name to avoid misfortune. Throughout the show, she meets misfortune at the hands of multiple characters with that character in their names, including and ending with her own mother, Hong Young-Ae (spelled 홍영애)
