We ask graduate students to write seminar papers in a variety of fields. Essentially, they have to learn enough in one semester to write a professional-level paper in whatever the topic of the seminar is. Ideally, this paper would be similar to one that might be published in a journal. Some students publish some of their seminar papers in second-line journals, in fact. The purpose of the seminar paper is to learn the process of becoming an expert in a particular field--even though the student will not really become an expert: 4 months is simply not long enough.
After grad school, we often just dig deeper into our own subspecialties. We become less adept at learning new subfields rapidly, well enough to write a seminar paper, but much better within our own niche. I was a very good undergraduate, but I would be very badly now at taking 5 courses in 5 unrelated subjects. I still have to know how to develop some limited degree of expertise in a short period of time. That skill never leaves you.
I'm getting a good feel for the field of Spanish American poetry now. Using what I already knew, and reading a few more secondary sources, looking at things a little more systematically, I'm maybe at 40% of where I want to be to write the book after next.