VS Librarian's Job

Recently I am selling a huge number of medical books to a school. The school's major is Oriental medcinen, so the books they are collecting are interesting. Not only new books but also the rare books like antique medical books in China, are holded by them.
My job is to find good books fitted to their major, and to sell them. After selling them, my interest usually goes to another business. I wouldn't be interseted in the sold book's future. Who reads it? How is it used? Whether is it useful or not? Such questions are over book-salesman's job.
However, recently my job is becoming close to the library, especially University's library, thus I have to think about the above once ignored questions. Because librarty's mission is to help students or teachers use books easily.

I have never studied Library science yet. So, the lack of the knowledge about it was my weakness. Especially, Cataloging is the most important and difficult knowledge. I heard from an old librarian that a librarian('s life) starts with cataloging, and finishes at cataloging.
Cataloging is the job and knowledge to organize the huge number of books in a library. The old man's remark was very impressive for me.

Last week, I had the chance to study librarian's job by chance. When drinking with some librarians, I asked them to teach me their job. They said, "OK. Come to our library. We will teach the whole process of our job."
It is rare that a book-salesman is interested in their job. That's why they might have been interested in me. Kindly, they made soon the two-day's study course for me.

The two-say's study was very helpful for me. I can't write down the detail here because it's too specific, but one of the impressive things was that Cataloging is related to the library's history.
I will give you an example. As you know, all books are categorised in a library. This book is in Japanese literaure. That book is in Philosophy. That one is in Biology. However, it is difficult to categorise the book with the title, "Postmodernity". When watching the title, librarians at first try to investigate how the book is categorised in other libraries. But, the most inportant thing is how the same kinds of books are categorised before in the library. Because, for students and teachers, it is useful that same kinds of books are on the same shelf. So, Librarians have to know their library's history.
It was a good experience for me to know the depth of their job.