I thought of this sentence last night: "Despite appearances, she's quite good-looking."
And now on to the real entry. When you really know a language, you have forged strong links in your mind between the sounds, or sequences of characters (depending on whether your memory likes to work aurally or visually), and the things they represent. One of the hardest parts of language learning is what we awkwardly call prepositions, because as my former lingustics professor said, they 'never quite mean the same way,' and they are extremely abstract concepts. For example, what exactly does it mean to be "on" something, considering all the ways that we use it? It's pretty difficult to come up with anything less than a list of different definitions, each with an explanation of circumstances in which it has that meaning. As a side note, consider the Sunny Day Real Estate song/album title "How it Feels to be Something On." Indeed.
Bear with me as I step into talking-out-of-ass territory, but the correspondence in Japanese is to certain of what they call particles (or rather, what they call what we call particles). Simply put, these are placed after words to signify the word's role in the sentence. Some are pretty simple, like wa, which indicates the subject of a verb. But others are rather strange, such as ni, which tends to be translated as 'to' or 'toward.' Some examples of verbs whose objects use ni:
iku 'to go' (the prototypical one)
kaku 'to write' (the person being written to is the destination of the writing)
au 'to meet' (the person being met is the destination of the action)
noru 'to board' (the vehicle is the destination of the boarding)
oshieru 'to teach' (the student is the destination of the teaching)
kariru 'to borrow' (the lender is the destination of the borrowing action?)
So in most cases some explanation can be arranged for relating it to 'to' or 'toward,' but in a lot of them we can not use 'to' or 'toward' with that verb in English, and some are truly bizarre. Of course, with the large number of homonyms in Japanese there is always the possibility of it being a different particle that happens to look the same, but I don't believe that is the case here, and I don't know if it happens much or at all with particles, since it would be very confusing. There's also the possibility that the Japanese idea of that verb is different from ours, for example that to a Japanese person, the action of borrowing has a 'direction' from the borrower to the lender. It could be that while we look at the trajectory of the thing being borrowed, from lender to borrower, as the direction of the action, the Japanese view the trajectory of the amount owed, which goes the other way, as the direction.
The other possibility is that the true definition of ni includes both what we translate as 'to' when applied to verbs of physical movement, and 'from' when applied to borrowing. This is fine, the only problem is it doesn't really get you to where a native speaker is, because when we say 'on' in English, we don't think of our whole list of meanings and uses. It seems to me that we do have some single coherent concept of what 'on' means, though it may be difficult to verbalize, that includes being on a physical thing, on a topic, on a task, and so on. So perhaps the best thing to do is simply present the verbs that use it and let the learner gradually form their own concept of what ni means.
As a footnote to these types of entries, I know that if a professional linguist were to read this, they would say that I am reinventing the wheel, and this has already been discussed in many books. This is true, though I have a minimal background in linguistics and am starting to acquire and read texts on Japanese linguistics. Of course if I am making my wheel triangular and really missed something here, don't hesitate to correct me. But regardless of the lack of innovation, this can only be beneficial to the language learning process, and perhaps to non-linguists who may realize the field has something more to offer than a sea of opaque terminology.