I'm going to write about history.
As a science fiction fan, learning that Isaac Asimov grew up in windowless spaces and big cities explains why he had no trouble imagining future humans living in domed cities or spaceships, a concept that seemed bizarre to many of his day. Learning that E.E. "Doc" Smith wrote the first space opera story, Lensman
, before there was even a market for it, and stuck it in a desk drawer until Amazing Stories
came along, explains so much of why it had such power; it was a strong, original vision rather than a reaction to a trend (and would go on to color much of future SF, most notably Star Wars
As an anime fan, discovering that Japanese science fiction grew out of detective novels explains so much of why mysteries are woven into so many modern anime series, even romance titles. Learning that Japanese film studios didn't have the money or resources for animation in the early 20th century (thanks to the many wars Japan was involved in) explains why it took so much longer for animation to mature in that country than in, say, America.
I'm fascinated by history, not as a general subject -- I rarely gravitate to history for its own sake -- but to understand cause and effect. I love digging into the history of a subject
(Photo by storebukkebruse on Flickr: https://www.flickr.com/photos/tusnelda/6140792529