Over the last three days, I've had three different people ask me to teach them how to crochet:
My roommate "S"
"S's" friend "A"
My sister "L"
"S" and "A's" request was spur-of-the-moment on Sunday night, so we had to scramble to get organized and find the right yarn and hooks for everyone in my stash. I learned to crochet from books and YouTube tutorials, so I didn't have any real-life models for teaching someone how to do this. It's a lot harder than you might think, especially when you're trying to teach multiple people at once!
"A" had a terrible time (not helped by her ridiculously split-y yarn) and finally gave up. "S," on the other hand, caught on fairly quickly and now loves it. New crochet buddy for me!
Then today, I gave "L" a lesson over Zoom. Within an hour and a half, she'd managed to complete several rows and switch yarn colors. (Coincidentally, she and "S" are both making Hufflepuff scarves, though with considerably different yarn.)
What made such a big difference? As far as I know, neither "S" nor "A" had ever tried crocheting before. "L," it turned out, had learned a little crochet in the past and had some vague muscle memory for it. In writing, we call that the audience's prior knowledge. "S" and "A" had none; "L" had a little.
This is an important consideration when you're writing nonfiction. The less prior knowledge your audience has about your topic, the more explaining you'll have to do and the longer it'll take for your audience to grasp the concepts you're trying to convey. This is why, for example, an elementary-school science textbook is so different from a college-level biology textbook. In elementary school, most of what the students are learning—including how to read!—is brand-new to them, so they need simple explanations of the most basic concepts of science. By college, the students have had years of experience with reading, have probably already encountered certain biology concepts (photosynthesis, cell division, etc.) in elementary, middle, and/or high school, and have developed the ability to think abstractly. Thus, college textbooks might need to briefly review the basics of biology, but they can soon move on to increasingly complex topics.
This is one of the reasons behind this bit of wisdom I picked up somewhere: "If something is written for everyone, it's really written for no one." If an author wrote, say, a brochure on buying the right ice skates and tried to target it to anyone who could read, such a broad audience will include people with vastly different levels of prior knowledge:
Readers from tropical or desert climates might not even know what ice skating is.
Beginning ice skaters have so much else to learn about the sport that they aren't yet ready for this information—they might not even know if they like ice skating yet.
Professional ice skaters and hockey players have probably been buying their own skates for years, so they either won't be interested in the brochure at all or will be bored and annoyed because it's telling them things they already know.
This imaginary brochure wouldn't do these three audiences any good!
So, when writing nonfiction, consider how much prior knowledge your audience has about your topic, and tailor your writing accordingly. If readers are new to the subject, explain terminology and proceed slowly from one concept to the next. If your readers are experts in the topic, feel free to use professional jargon and refer to common theories or principles that experienced members of your field should know.