Return the spoils of a mistake
I will return it. Even a gentleman thief does not consider stealing from an innocent person to be in good taste.
You paid ¥1,000 for a ¥500 purchase, but received ¥4,500 in change by mistake. The cashier hasn't noticed. What do you do?
I will return it. Even a gentleman thief does not consider stealing from an innocent person to be in good taste.