My two favourite quotes are from Episode 9, and they both require a bit of context. (I italicized the best parts~)
Mago: You nearly died because of Man-wol. I heard you embraced that potent curse. If you haven’t lifted that curse, your soul is probably seriously hurt now.
Koo Chang-sung: Jang Man-wol protected me. I’m fine.
Mago: Man-wol is fine thanks to you. You are the one who protected her. My sister chose the right person. So keep up the good work.
Koo Chang-sung: Was I sent to that hotel for that purpose? When the terrible fate comes to her from the past, am I supposed to block her from it?
Mago: You successfully carried out your mission. Why are you angry? Do you feel pity for the Man-wol you saw in your dreams?
Koo Chang-sung: Yes, I do. I feel angry that you praise me for not taking her side. She abandoned me because I got in her way. Are you telling me to keep on getting in her way?
Mago: It’s cool to take someone’s side, while getting in the way is not. Everyone wants the role of embracing and consoling her. The shabby role of getting in the way, holding on, and begging can only be done by a good person.
And my other favourite is this one:
Spirit of the Well / Daedong Spirit:
I ran away from there. I am scared.
…
I am scared of getting abandoned.
I have never dried up and have given the people fresh water. No matter how much they took, I was filled up again. I gave them water to make alcohol and let them make money. However, I can no longer fill up as much water as they want. I am continuously getting dried up. I ran away before I dry up completely and get abandoned like an empty pond. I chose to abandon them first while they could still miss me.