The real world is far more complex and ambiguous than most story universes created by an author. Take the controversial topic of cannabis, for example. So many conflicting opinions exist, and scientific findings are not absolute. Yes, one study finds correlation between cannabis and cancer (which doesn’t exactly mean, that there is causation involved), and some lab studies discover that cannabis kills cancer cells. Does cannabis cause psychosis? Oh, only with predisposed people. But does it either trigger the dormant psychosis at once, or is there an accumulative effect of ongoing cannabis-consumation?
There are no clear scientific results, and everyone, based on what they are arguing for, or what they tend to believe in, give more emphasis to some findings over others, which they compress into short, absolute sentences. These statements in turn are taken in by other people, who continue argumentation based on these simplifieds truths – not that they aren’t true, but they are not all the truth. Or, in other words: Everyone is right, in some way. But there are always more details to consider. There is always one more little side fact that relativizes the arguments laid out before.
This is especially potent in medical areas (of course, jumping to conclusions here 😉 ). But basically everything in the world that has not been invented by us humans, that is the subject of our ever ongoing investigations, is subject to haziness. It can not be put in simple words. (As for findings in physics, that appear absolute: In the end, they are always models which simplify to some extent).
But counter to these real-world situations, when an author creates an imaginary world, often they deal in absolutes. One is good, one is evil. The medical drug is 100% effective, but still the autorities want to conduct tests, so the patient who can only survive with this drug wouldn’t know whether they get the real drug or a placebo (since it is a medical study they’re partaking in). Or a person has a strong mindset, being stern and always of the same opinion. The hero has a clear task, and that is undoubtedly the right and sincere thing to do.
But in truth, everything is hazy. Even your most idolized character, whether real or fiction, has contradiction within themselves.
Opting for simplicity in fiction stories makes it easier to develop and to tell them, and eases their understanding in the audience. It just sounds so much better, when the written words go for an absolute. “It is this way” is much nicer to read than “It is somewhat like that, but you must consider this additional piece of information, that doesn’t make all the difference, but adds some depth to the first fact, that you need to know”. Phuh.
But without the real-world ambiguity, something is always missing. It’s not real, or as we say in regard to fiction: It is not authentic.