It was difficult for her to forget her first failure.
Out of all the other subjects, Cynthia knew that Yang would differ from the rest. She knew she would have to keep a closer eye on him than all the others. But even though she was extra careful, she could not predict that he would choose to stay despite completing his mission. She could not foresee that he would end up killing somebody.
She let her guard down. Once the mission was over, she did not think that anything bad would happen to him. All his obstacles and trials are over, what harm could come his way?
During that time, a subject with a rare reaction to the kaleidoscope appeared, and she focused on them for a while.
As a result, this led to her neglecting Yang. By the time Cynthia realized what was happening, Yang had killed more than one person.
