For one, all the sources are basically things I have around the house. I sit in my living room and drag books back and forth. What I don't have on my shelf, I can find in online or computerized databases, which mostly have very sophisticated search options (and are more accurate than, say, JSTOR, in my experience).
And for the other - it's like I'm writing the paper from end to beginning. Usually, you read through sources and then construct the ideas. Here, I know what I want to say, and then I have to spend time looking for the exact source. Like, I'll say to my father, "what story from the Gemara do you think illustrates this point?" and he'll say, "well, how about R' Elazar ben Arach?" and then I go look it up. Or I'll have a quote in mind I want to use, and then have to go and figure out where it actually came from.
It's amazing how much "general knowledge" about Judaism is crammed into my brain, and how difficult sourcing some of it is! But the amazing thing is that I AM managing to track down these quotes. Nothing came from vacuum, and it's impressive to see how ideas have developed and shifted over the centuries :)
(gah I want to get done with this paper already!!)