The word "sumimasen" 済みません has been described as "the most useful word in the Japanese language". It's often described as meaning "excuse me" or "I'm sorry", and it serves quite well to apologize for bumping into someone or to get someone's attention.
But I was puzzled when I bought something at a little shop in a shotengai in the Osaka suburbs and the shopkeeper said "sumimasen". Was he apologizing for ripping me off? I learned later that the word is often used to mean "thank you". We might compare it to "sorry to trouble you".
But it's interesting to look a little deeper. That "-masen" is a negative verb ending, it means something is not done or is not the case. "Nihongo ga wakarimasen" means "I do not understand the Japanese language." (True, and a very useful phrase for travelers!) "Biiru ga arimasen" means "There is no beer." (A very sad sentence, desu ne?)
So, what is it that is not the case here?
"Sumu," (済む) the base form, means "to finish" or "to come to an end". According to one explanation, the use of the negative form as an expression has roots back to the samurai days of the Edo period, when the economy was getting complicated and there was a lot of buying and selling and lending and paying back going on. When accounts were settled and debts repaid, it was "sumu," done, finished, cleared, all wrapped up. If a debt still remained, though, it wasn't sumu, it was "sumanu" or "sumanai", or in more polite form "sumimasen".
Of course, as with most expressions of this type the etymology doesn't give a perfect account of the meaning. But I think it's not completely wrong to say that one of the most often used expressions in Japanese is something along the lines of "I am in your debt"; a reminder of the network of social obligations that ties the society together.
Kaicho Nakamura, the founder of Seido Karate, often talks about "kizuna" -- relationships, or bonds, in this case the bonds that hold us together as a community of martial artists. I think it's important to think about these bonds being created in specific acts, specific interactions. When my sensei or a senior instructor teaches me something, I am in their debt. How do I repay that debt? (The same, I should note, only goes even more so for my first and greatest teachers, my parents.)
In mainstream American culture, and I think to a large extent also in modern Japan, the answer would be money: I'm the buyer, the teacher is the seller, I paid for my classes, give me the knowledge, the service I bought, and it's all settled. It's a simple free market transaction, right? No need to bring human feeling into it.
That's ok maybe if you're hiring someone to mow your lawn or paint your house. You don't have to have much of a relationship there -- though you'll probably get a better paint job or a neater lawn if you do. But when one person teaches another, that teaching can really only happen if there is a relationship. The teacher has to understand the student's perspective, how the student thinks, their strengths and weaknesses. The teacher and student are a team. You can't measure that relationship in money; trying to settle that debt with dollars is as hopeless as trying to put good deeds in your car's fuel tank.
Which is not to say that teachers don't need to be paid in dollars as well. The bank that holds my mortgage is uninterested in human relationships and networks of obligation, so financial support is necessary. But no one human enough to be a teacher can get by on dollars alone -- "not by bread alone", as the cliche goes.
I try to pay it back by teaching what I've learned, but this debt will never end. It is not finished.