Long ago, before I went to library school and immediately after I'd graduated from college, I worked for a year in my hometown public library in order to determine whether or not I wanted to make a career of it. I'm no longer sure of my job title then ... it was something like "senior clerk" ... and the year proved invaluable inasmuch as I learned the "backroom routines" of the day.
Typing hundreds of catalog cards pretty much convinced me that I wanted to work in reference. That was, however, off limits since I didn't have a masters degree (yet). But I watched and occasionally learned.
One of our reference librarians was a very nice Chinese lady whose grasp of English was adequate but whose American cultural experience was limited. A patron came to the reference desk and asked if she could help him with his carburetor problem.
That was something outside her experience. She repeated the word, slowly, a couple of times and asked him what this was ... and eventually learned that it had something to do with his truck. The patron in turn learned that she hadn't a clue about what he was looking for and made the (rather natural) assumption that he wasn't going to get much help from his library. He left before she could explain that the library owned many things about trucks (which was as far as she could go since she had no idea what a carburetor was).
Meantime, the mere clerk (me) was frustrated because he couldn't really speak out. I knew what a carburetor was. Heck, growing up blue-collar and male meant knowing quite a bit about carburetors. I also knew where the various repair manuals were.
The lesson I learned was that it was at least as important to understand the question as it was to have access to the books.