Below is tangent graph in relation to circle (R=1)

below is all six trigonometric functions on unit circle (R=1)

The original tweet summarizes it pretty well. Fanfic tends to be popular among certain types of neurodivergent people (aka people most likely to read excessively as a child, and have burnout as an adult) for the same reasons that we tend to hyperfixate–neurochemical signaling (I hope I’m using that phrase correctly). What I mean is, for people who are really dependent on changes in dopamine/serotonin/neurotransmitter levels, who have low levels or wonky neural reward systems (perhaps the most common types of neurodivergence)…people like us rely on dependable external sources of those neurochemicals. In order to function, we spend a lot of our free time trying to level out our brain chemistry using things that can reliably bring us a steady stream of joyful moments (rewards) without costing too much of the mental effort that is already in short supply. 

significantly: the investment of reading has to be balanced with a steady “return on investment”–and this return has to start fairly quickly. because again, we don’t have a lot of attention/energy to invest on tiring things. we have perpetual “low batteries” in that regard.

that doesn’t mean these stories are “simple,” or that they lack complexity or value–only that the reward has to come in short regular intervals, and it has to have a low “upfront cost.” these stories are only “easy” to read in the sense that the effort we put into them is rewarded in a timely manner. which is why fanfic stories are so perfectly formulated for neurodivergent readers–they are often beautifully written, but skip a lot of the upfront costs (of introducing new characters, of world-building, of getting the audience emotionally connected to the story elements).

the nature of fanfiction is that the reader has a pre-existing relationship with this world and these characters. that–combined with the shorter average length of fics–means that fan fics very quickly start rewarding the reader in a way that traditional fiction struggles to. that’s not a bad thing! and maybe it’s something more traditionally published writers should be paying attention to.