After years of research in secret, the government was finally able to create the first machine that was perfectly human-like. Nothing about the machine looked off, inhuman, or imperfect. They called this Humanoid Oh Sehun. They programmed this machine wtih emotions, common sense, high intelligence, and a number physical abilities, but during the process, they made a grave mistake that would cost them one of the most important assassin missions in South Korean history. 

So what exactly was this mistake?

They allowed this Humanoid to learn.