Yesterday afternoon, a student told me a story about her work at a popular casual clothing retailer. She said that there is a man who is well known at all her employer's branches for trying to pull a trick on them to cheat them out of money. The man buys an item of clothing, takes it home, damages it slightly (e.g., a small tear), and then returns to the shop he bought it from to lodge a complaint. When he complains, he insists on getting his money back and keeping the damaged garment.
My student said that this man keeps using different names when he pulls this stunt at various stores, but his face is well-known by now. While this trick initially worked due to the Japanese desire to please the customer and their squeamishness with being confronted in anger, it is no longer effective since it has become clear that he is a petty con man.
I used my student's working experience as an opportunity to teach her the term "con man" and she asked me why such scammers were named so. I explained the origin of the term to her, but afterwards I got to thinking about how teaching English requires you to have some understanding of the origin of words and terms in your own language that not all people possess. I wondered how many people understand the origin of "con man" who are not British. (I'm pretty sure that most British folks know it because I've heard it used in its full form (confidence trickster/man) in British television shows.
The sad thing is that a lot of teachers who don't know the answer to a question regarding grammar or the origin of a word will simply say, 'that's just the way it is,' rather than admit they're not sure why it is that way. Generally speaking, that's probably not such a big deal, but being able to explain things properly does help the student learn more effectively and remember the meaning of the words better. If I tell a student the "con" in "con man" comes from "confidence" because the scammer has to gain the confidence of his mark, she's far more likely to recall the meaning when she hears the words on a T.V. show or in a movie than if I just tell her, "that's just the way it is."