Some people think, when they are able to understand 5 words in a drama/movie/song, that they probably should share their wisdom with everyone else. Either that "everyone else" wants it or not. And they base their opinion on "what I think". Sorry to disappoint you but "what I think" methodology is wrong. Of course, in scientific research this approach is very appropriate under one condition - one needs to have the background for it. And background is not "cause I think so". The background is - getting familiar with the whole methodology. I hated this word during my MA studies, but now, when facing PhD, I feel like I'm in a deep hole because I lack the methodology. Fear not, I'm finding it slowly (some hawt guys don't make it any easier, but whatever). But to develop one's own approach, finding out more about the background - this is what's most important. You can't write a thesis about the dark matter (astron.) basing on your own thoughts. You need to read the results of someone else's research. Every great idea in the world comes exactly from this point. One is either against it (and proposes one's own interpretation of the matter), or agrees on it (and proposes the developped and deepened version of it).
This is why I'm annoyed, and probably not only me, of those who claim to know everything on some topic, basing on their own limited knowledge. You don't need to read all books in your library, that's not the point, but do some research on the matter that interests you the most.
In my Department there is this summer course on japanese anime. From what I know, the course is great, lots of people enrolled and so. But there is this slight problem. Some of the participants were bored to death when during the course they had to listen about pre-war animation in Japan, and watch black-and-white short movies. They expected to watch Bleach all the time I guess (or whatever that is so popular, I have honestly no idea) and dissolve their fan-selves in one, communal KYAAA. Well, what did they expect from the course titled "The History of japanese Animation"? The crucial word "history" was probably overlooked.
The same thing is when I conduct my Culture courses. Some people probably expect me to show them some fancy castles, few temples, geisha and Harajuku. I do show them that, but after the horror of history. This is this background. You can't understand the modern country without knowing, even a little, about its past. It would be like doing integral exercises without mastering basic math operations (you know, 2+2=4). There's no way in hell you can do it, trust me.
The background would be to face other people's opinons. Either you agree, because there is no shame in that, or you may disagree. While disagreeing, retort like "cause your theory is just stupid", or "that's not true" are simply against common sense and basic elements of the rhetorics. You can't say someone else's theory/words are stupid, because this may imply that the person him/herself is stupid. And this will put the person who says that in the position of some obnoxious jerk who likes to throw words without thinking, and no one, really no one, will take words of such person seriously. Also, saying "that's not true"... oh, this is a heavy one. It implies the ignorance of the person whom those words are directed to, only because the person who says so thinks differently. "That's not true" is the statement indicating: "You have absolutely no knowledge whatsoever, but listen to what I have to say. It's an Absolute truth. And kneel, you knave!" While bickering over the opinions, we should really be careful with the words.
And now the real topic. I read yesterday on some blog that Korean borrowed words from Japanese. At first I was "OMFG, LOL", but then I was "WTF??" The answer is simple as the flail construction. Both languages borrowed from Chinese. They sound similar, because both ancient Koreans and Japanese heard the same sounds. In some period of the history in both countries, Chinese held the position equal to the Latin in Europe. It was the language of the literati. Both languages in their native shape didn't have the vocabulary related to more complicated socio-political-religious elements of life. The best example? The numbers. Native numbers in Japanese end with 10 (Korean does have some others for full decimals, like 20, 30 etc.), everything above that was considered as "many". When the countries became states, the full system of administration (just to name this one) was needed. Both Japanese and Koreans (well, actually Goguryeo, Shilla, Baekje) borrowed already existing solutions from Chinese and changed them according to their native customs.
Yakusoku in Japanese and yaksok in Korean sound similar, right? It doesn't mean one borrowed from another. In Han Chinese, the word "promise" sounded probably something like that (I don't know the classic Chinese though, and to compare you need to refer to the period before 9th century AD), and both languages not having their own word for that (or finding the chinese version more fancy) incorporated the word into their own lexicographical system.
If anything, it would be the other way around. In Yayoi period (appr. 250 BC - 250 AD) three migration waves hit Japan, and the biggest wave was from the continent. New people brought with them rice cultivation, potter's wheel (just to name two most important innovations), and continental knowledge. Later, Chinese scripts came to Japan from two Korean monks (one was the teacher of the further emperor Ojin), not to mention the great surge of refugees after the fall of Baekje in 7th century to Yamato (let's be frank, Yamato was just a confederation of powerful clans then, and they knew nothing about Kanto plains). To say that the borrowing was other way around shows some really disturbing lack of common knowledge. There was no migration wave from the archipelago to the continent.
I will say it once more: both Korean and Japanese borrowed their similar sounding words from classic Chinese. Period.
But if anyone wants to look deeper into the origins of both languages: Japanese originates from Korean. Some people won't be happy. One more proof? Well, Japanese used in the times of Kojiki and before (712), had ie. two vowels "e" and two "i". We don't know how they sounded, but the scientists are sure about that (quite new research, hints of that were visible before WWII, but the real development of that theory began in the 70's), according to the article of Timothy J. Vance, The Etymology of Kami. Modern Japanese has poor phonetic system, and only 5 vowels. Let's not delve into Korean vowels horror. But in preliterate times, the similarity between Japanese and Korean was more evident.
I was always wondering in the days long past why there is Kwaidan, Kwannon etc. A little bit research, and comparison, and no surprise - this sound of "kwa" was in use even in 19th century Japan. Some people could jump into the conclusion - of course! Korean borrowed the syllable "kwa" from Japanese! Well... you see, Kwannon (modern: Kan-on, chinee: Kuan-in, kor. Kwan-eum) is a buddhist bodhisattva. And Buddhism came to Japan in 538 (or 552) from Baekje. The theory is invalid.
Have a nice day!
