"Yes, I didn't do it"

One thing I had to learn about the Korean culture is best to avoid negative questions. “Yes” and “No” have the opposite meaning when following a negative question in English than in Korean. The dialogue I had with my co-worker went as follows:

Me: “Daerinim, didn’t you finish the statistics report yesterday?”
My co-worker: “Yes.”
Me: “May I please have it?”
My co-worker: “But it’s not finished yet.”
Me: “But you just said you finished it yesterday.”
My co-worker: “What? I said no.”
Me: “You definitely said yes.”
My co-worker: “Yes, because you asked me if I didn’t finish it yesterday. That’s right, I didn’t finish it yesterday, so I said yes.”
Me: “That’s quite confusing. In English, it means the opposite. If we say yes to a negative question, it means ‘yes, I did finish it’. If we say no, it means ‘no, I didn’t finish it’.”
My co-worker: “Isn’t that illogical? Minus times plus is still minus, but minus times minus equals plus.”
Me: “Could it be that you read too many math books, my friend? I guess English is just consistent within the sentence we speak. Yes is always positive and no is always negative. We don’t mix language with mathematics.”
My co-worker: “Well, I guess in the Korean language, we rely much more on context than in English.”
Me: “Yes, that's what makes it difficult for each of us to learn the other language. Anyways, I promise not to ask any negative questions again.”

Picture: Sunset taken from Seoul Namsan Tower