My first comment is definitional. Technically there is a difference between a library and an archive. It is different to work with a manuscript book and documents. But technical categories aside, the tasks and difficulties are much the same, so I'm going to lump them all together under the rubric of archives.
My second comment is that working in archives can be hard. It takes a lot of concentration and patience and a high frustration level. And when working with pre-early 18th century material, especially in foreign languages or foreign scripts, the first time looking at a new kind of writing is liable to be a pretty awful moment. I don't think I've ever met anyone, male or female, who did not feel like crying (and many who did actually cry) the first time he or she went to an archive to work with this sort of pre-modern material and came face to face with a document and stared and stared and couldn't make heads or tails of it. There are ways to make the process easier, and that's one of the things I want to discuss in a future post.
On the other hand, it is an exhilarating, addictive feeling to turn a page and find a gold mine, especially if it's a gold mine you didn't expect and no one else knows exists. And, frankly, there is something thrilling about holding in your hand a piece of paper or parchment that someone else created hundreds of years ago and letting it speak to you.