In "Bluebird House" the reason why Kim Hye Sun abandoned Chae Soo Bin was revealed. This too was out of motherly love.
On the episode of KBS2 weekend drama "Bluebird House" (script Park Pil Joo, director Ji Byung Hyun) broadcast on August 1st, Han Eun Soo (played by Chae Soo Bin) demanded why her birth mother acted in such a way. She demanded to Lee Jung Ae (played by Kim Hye Sun) why she would abandon her own blood. She also inquired why she would not even look for her.
To Jung Ae, Eun Soo said, "Why did you abandon me? I want to listen to why you threw me out." Jung Ae said, "It was just difficult. Just." And didn't answer. When asking why she'd be curious. Jung Ae said that she shouldn't try to be curious.
Nonetheless, Eun Soo said, "But why are you trying to be so responsible for Eun Ha." Jung Ae said, "I know what you're trying to say. But it was so hard. No particular reason but it was very difficult. So that's what happened. I had nowhere to abandon Eun Ha so I had to raise her. If there was another person like Sun Hee, I would've abandoned you, you know."
