Sang Eun's past

In the sixth episode, there's a line that bugs me so much about Sang Eun: 

We tend to brush off Sang Eun's reactions because usually after such dialogues like this, she would inject some quirkiness. 

But I have a feeling there's something deeper here. 

Another instance: 

At first I was thinking maybe it is just because she is upset with Ji Ho so her responses tend that way, but if one would observe her in the past six episodes, she tends to act tough and hates sympathy. It almost feels like she is always on-guard about how she must be perceived. It feels like she's afraid to be seen weak and dependent, probably that is the reason why she chose her business, because it is her insecurity. 

So long as she could comply with the client's requirements, she feels like she's doing things right. In short, it's like her 'security blanket', something reassuring for her. 

What causes it? We still never know the whole backstory with Madam Yoo. What matters now, we are seeing that she is finding solace in Ji Ho's presence. 😌