More specifically, I've painted various landscapes (and am working on one right now) that are somewhat pleasing. I can look at them and derive pleasure in a way that I don't from my representational paintings of humans. Many theorists, both in art and otherwise, say this is because humans are attuned to the proper proportions for humans, and something inside of us instantly reacts by saying "something ain't right here" more intensely than we do about, say, tree stumps. Tree stumps come in all shapes and sizes, and we generally aren't worrying too much one way or the other about them: they aren't going to attack, we aren't evaluating them for suitability as mates, etc.
Currently I'm muddling along in terms of painting realistic humans and humanoids. They're fine for a beginner, but the basic proportions are simply wrong. This might not be noticeable if I were aiming at a clearly surrealistic style, but aiming for realism? There are reasons people spend years trying to master that, and many never get there. I practice, both drawing and painting, and I'll get better in time, but let's just say I'm very glad that I take pleasure in the act of it.
How does this apply in writing? We often talk about characters being cardboard when they aren't fully rounded, though individual readers' tastes may not be troubled by individual characters' realism. Does one hit the revulsion factor, though? Not really, not for any piece of fiction across the board. My assumption is that this is because there's something about how we perceive images that differs from our language perception. Likewise sound, I suppose; dissonant music catches our attention because it's wrong on a level of orderliness that's ingrained. One can become inured to it, as I assume one can become hardened to (genuine) screams of pain on a battlefield or in an ER, but it presses a button right off the bat for most people.
Different genres have different conventions in terms of what constitutes a successful depiction of a human, and lack of awareness of these conventions on the part of a reader can lead to failures of appreciation. Lovecraft's characters, and much fiction written in his footsteps, is not rife with either authentic or effective dialogue. Sometimes the conventions amount to differences in perceptions of what constitutes life -- and thus some reviewers complained that the characters in The Sun Also Rises just sit around and eat and drink. Lord knows, more ink has been spilled on men who write women badly, white people who write people of color badly, etc. I'm conflating genre conventions and different life experiences here, but both go toward what makes a work plausible. We often forgive stories for minor mistakes or flaws, but everyone has their point of disengagement from a work: that moment where you stop caring about the work because of something in it that you just can't get past: impossibly shrewish women, implausibly iron-thewed swordsmen, lives so banal they defy the human experience of pleasure.
In so far as a painting is trying to tell a story about people, it can't do so without articles (foreshortening), parts of speech (proper proportions), or punctuation (compositional flow). Many paintings are about things other than telling stories, though often they tell more of a story than we may think. Warhol's cans of soup, for instance, have a story behind them, for which the paintings are signifiers. I still struggle with telling effective stories and narrative flow at times, but I have ideas about proper "proportions" on the page, and an awareness of what proportions are right for picaresque contemporary novels, science fiction short stories, horror movies, etc. In these cases, the uncanny valley is contextual rather than absolute.