Why does Pierre claim he can't beat Joja's cheap prices when they sell seeds more expensive? Easy! As an independent businessman, Pierre can modify his prices just for you. After all, after you've set up you're coming in at the start of every month buying several hundred seeds, his wallpaper catalogue, and backpacks. As for the cheaper cooking goods, that's because he likes you. Morris has no such flexibility as he can only sell at JojaMart's inflated prices until you have a membership, and even then they're identical to Pierre's.
There's a deeper level of brilliance here. JojaMart is essentially a supermarket, and as such they carry typical supermarket goods. The kinds of things you buy as a farmer are not typical merchandise for them. They still want your business, but they don't have the supplies or the connections at that location to sell at the prices of Pierre's store because Pierre actually runs the kind of store that routinely stocks those goods. Instead Joja has to have all that stuff specially shipped in. The extra money you're paying until you get the membership is essentially shipping and handling, which gets waived with a membership because then Morris knows you're interested in shopping with them and starts stocking it.
Another way to look at it: Joja sells produce (to the other villagers) at cheaper prices than Pierre's, and sells you seeds at steeper prices - which means that, if it was up to Joja, you'd be forced to buy high and sell low, and that is certainly a way to discourage independent farmers and traders like yourself.
Joja Cola doesn't restore much energy for a caffeinated beverage. Well, the most likely place you're going to find it is as fished up trash, since it's insanely overpriced in its vending machine. Everybody in town except Sam dislikes it, and they're throwing their cans away half-empty!
Also, Joja Cola is the only item categorized as trash which cannot be recycled into anything useful. It's not just garbage, it's irredeemable garbage.
Maru has diamonds as one of her favorite gifts, and at first glance you wouldn't think someone like Maru would be into superfluous gems, but then you take another look at what she likes and dislikes and you realize, as a scientist, Maru would need rare gems and materials for her and her dad's projects.
Take a look at the projects Maru and her father do: Maru does a lot of practical applications, building, and the like, whereas Demetrius is more observation and taking notes. You'd think a scientist would love Battery Packs (as Maru does), but Demetrius hates them. Look at what he does: Research and a lot of writing. Of course he doesn't like them, they're useless to him. Speaking of batteries, why does Maru like gold bars? It's because gold is one of the best conducting metals in its pure state, perfect for wiring in mechanical devices. That's probably also the reason she's one of the only two people who likes copper bars as a gift, while almost literally everyone else dislikes or hates them.
Haley has diamonds as one of her liked, but not favorite gifts, which at first glance would seem strange for a girl into clothing and accessories, but that's the point: Haley probably has a large amount of jewelry already and while she still likes them, it is still dulled down a little because of it.
Haley is also the only villager who doesn't love the Prismatic Shard; in fact, it's one of her hated gifts. Presumably a fashion-conscious girl like Haley would find the bright, contrasting colors of the shard to be tacky.
One of Sebastian's favorite foods is Pumpkin Soup. And where do you get the recipe for Pumpkin Soup? From befriending his mother, Robin! The guy must really like his mom's home cooking. One of Seb's lines in the Fall season has him griping about "pumpkin spice everything". This isn't just simply him going against a trend; Sebastian knows (and likes) the authentic taste of pumpkin.
On a more somber note: Penny's hated gifts include wine and beer. With her mother being an alcoholic, that shouldn't come as much surprise. Her dislike of grapes may seem odd until you quickly realize that wine is a product of fermenting grapes. There's also the fact that she hates the Rabbit's Foot, while everyone else loves it. Maybe she's an animal person... On a brighter note, among her favorite gifts are Tom Kha Soup and Sandfish. These seem out of place; especially compared to her more modest favorites, the Red Plate (Red Cabbage and Radish), the Roots Platter, Poppies, and Emeralds; and would be easy to write off as someone who's lived poor wanting a taste of something exotic. Except that these items are found in Calico Town, on the bus line. The bus line her mother used to work before it broke down. It's easy to gather that these foods were probably brought back when her mother was employed, and remind her of happier times.
Marnie's list of loved items include pink cake, farmer's lunch, pumpkin pie... and diamonds. The last one seems a bit odd for such a down-to-earth woman, doesn't it? Until you get to know her (and Lewis) a bit better. She's an old maid whose "boyfriend" insists on keeping their relationship secret. Which means no engagement ring.
Abigail's love of pumpkins is obvious when you find out how much she loves the fall season. She also loves Blackberry Cobbler, but hates Blackberries. This makes more sense when you realize that giving her a blackberry implies that she'd need to make the Cobbler herself, which itself implies she'd need to stay home / stay safe / act like a stereotypical girl, as she puts it. As shown in her 6 heart cutscene, she tells her father that she hates being treated as such. Another possibility is that Abigail doesn't like the taste of straight blackberries very much, but loves them when they're cooked into something. It'd be like a person loving banana bread (with the sugar, spices, nuts, etc), but not being at all fond of bananas as a fruit. Her love of the Amethyst becomes obvious as the color matches her hair. Her liking Quartz, similarly, isn't too far off.
Leah's the only person who likes Driftwood, which without a Recycler is otherwise completely worthless. But a Nature Lover like Leah would probably find a couple uses for such a thing, either as material for her work or as fuel after it's been dried out.
Shane's love for hot peppers and spicy food: being drunk numbs the sense of taste (among other things), so he may be craving anything flavorful. Hot food also encourages drinking more, and studies have indicated a possible link between an affinity for spicy food and an increased risk of addiction/alcoholism. Ties into his depression as well; spicy food isn't unheard of as a coping strategy for a number of reasons. The intense taste might make him feel more alive, and the pain of capsaicin burn can be handy as a safe way to sate self-harm urges.
Could the reason that Krobus hates being gifted a strange bun despite the fact that Shadow Brutes drop them be because he realizes the implication of the Farmer being in possession of one? As in the implication that the Farmer killed a Shadow Brute to get one?
Jodi loves receiving dishes of food (and diamonds!) from the player. Considering how often she gripes about having to do chores and the sort for her family, you handing her plates of food probably saves her plenty of time and energy to do what she wants! Also, one of her favorite dishes, Crispy Bass, is Kent's recipe. So it probably reminds her of happy times. Alternatively, she probably exhausts herself by doing all the housework, and recovers energy better with cooked dishes!
While Kent's loves are dishes his mother used to cook for him, he likes springtime flowers, very odd for a man like him. But he returned home in spring from being in a prison camp. Consider when he came home: the beginning of spring. It probably reminds him of no longer being in the prison camp.
The Wizard doesn't like Strange Buns. Strange Buns are used in his ex-wife's dark rituals.
A good amount of Emily's dislikes and hates are stuff that involves fishnote aside from the universal hates, the only gift Emily hates that doesn't involve fish is Holly. While Haley's more vocal about how she misses their parents (who have been traveling for two years), Emily's dislike could come from the same place: there's no indication that there's an airport nearby Pelican Town, so it's very likely her parents are traveling on the water.
As for most of her loves being gemstones? Considering that Haley has so many that diamonds are merely a liked gift for her , she's probably thrilled to be the one getting them for once. Alternatively, given that she's shown to make clothing (and wool and cloth are also some of her loved gifts), it's probably because she enjoys using gemstones to make clothing (quartz being merely "liked" as opposed to "loved" mainly because it's not as useful in clothing/jewelry as, oh say, a sapphire or ruby).
There is a shrine that turns unwanted children into doves and erases the memory of them. Considering you find it in the Witch's Hut, it may explain why the Wizard had an affair. It seems the shrine can only be activated by someone with a close bond to the child, such as a parent or guardian. The Wizard knew this and wanted a child the Witch couldn't transform, so he cheated on her then left the child to be raised by someone else.
The Wizard only suspectshis child is one of the villagers. While this could be normal uncertainty about such a messy situation, it's possible the Witch actually used the shrine to erase the memories of those involved. However it wasn't a perfectly clean wipe and all involved remember something about what happened. The Witch remembers everything because she's the one who used the shrine; the Wizard remembers parts thanks to his magic and piecing things together; Caroline remembers enough to feel wistful about her time with the Wizard; and Pierre remembers enough to be suspicious of the Wizard and Abigail's parentage.
The reason why the Player Character can function on so little sleep is because they are an ex-corporate worker. Seeing how someone died while working for Joja and they didn't even bother to clean up the corpse suggests that Joja squeezes every ounce of sweat and blood out of their workers. Working at a farm might just be light work for the PC.
The starter watering can is capable of watering 40 crops on one fill, which is exactly the maximum number of crops you can plant on Day 1.
Why does Sandy like all of the movies at the Movie Theatre, from the childish-looking Brave Little Sapling to mature films like It Howls In The Rain? Well, she did say she wanted a reason to come out to Pelican Town, and you inviting her to watch a movie is reason enough, regardless of what kind of movie that's playing.
The Dwarf also likes all movies. The Dwarf lost their family in an attack by the Shadow People, and is an outsider to the humans. They're probably just happy to have a friend. It may also be that the Dwarf has lived their entire life underground in the Mine, and so is simply taken with the novelty of movies in general. New foods, bright, moving colors on a screen, the whole thing is likely new and exciting to them.
Krobus dislikes almost all movies. Krobus has a light sensitivity. The bright screen probably gives him a headache! The one exception, Mysterium, is in black-and-white, so it's probably easier on his eyes enough for him to enjoy the movie a bit.
One of Penny's heart scenes shows that she's really bad at cooking. Given that Pam lives on pub food and TV-dinners and the father left, she's never had the opportunity to learn from someone. If you marry her, Penny learns to cook better food for you— either you're teaching her, or she's watching "The Queen of Sauce" while you're out working.
It seems odd that the lava pit at level 100 of the Mines has so much trash in it, but consider that Pelican Town has no garbage disposal service. Presumably, all the town's trash is dumped into the lava pit. As for why it doesn't burn up, chalk it up to Gameplay and Story Segregation.
For a small town, Pelican Town seems to have quite the unemployment problem, with Jojamart easily being the biggest employer (including the nameless NPCs who work there). This is a sad truth about real life small towns - no wonder the protagonist's parents didn't stay there. Little to no job opportunities.
So why wouldn't anyone else take up farming? Note how the PC and Marnie seem to be the only ones with any kind of land that extends more than 10 tiles beyond their house, combined with the fact that they don't have much money. In real life? Farms are quite expensive... but there aren't a lot of profit margins to be had there.
For some reason, Shane loves being given a cup of Joja Cola at the movie theater, even though he hates being gifted the cans of it just as much as everyone else save Sam. One possible explanation is that Shane only dislikes being given the cans because they remind him of the job that he hates, where he probably stocks them all the time, not because he doesn't like the taste.
Although the player character proposes to one of the bachelorettes by giving them a Mermaid's Pendant, proposing to another player instead requires them to craft an engagement ring. This makes sense when one considers that the Mermaid's Pendant is a local Stardew Valley custom, and the player characters are all outsiders to the valley- they would naturally expect a traditional ring proposal, and wouldn't understand what the pendant was supposed to mean. ConcernApe even confirmed this.
At the saloon, Shane doesn't go to a table or a spot at the bar, preferring a corner by the fireplace. Just him being his solitary self? Maybe, but there could also be more to it. Depression interferes with thermoregulation, especially against cold. Shane is rarely seen without a hoodie on, even in the summer, so he might be there to stay warm.
Broken glasses are a common trash loot from fishing, but where ALL of them come from? The only NPCs with glasses are Harvey, Maru, Pierre, Gunther, and Morris (and Mr. Qi if you count in sunglasses), not exactly many enough people to need that many glasses per year. However, there is a pointer on who might be the culprit: all broken glasses have round lenses. While people may wary their glasses styles, people tend to like a specific personal style. Who is the one with round lenses? Morris! The local "quantity over quality" person. He probably has a bulk of poorly made glasses that he keeps discarding when they break.
Joja Corp doesn't bother to clean up the corpse of your dead coworker at his desk in the intro (or, in the censored version, label the empty desk as "terminated"), so they clearly don't care about employees dying. When you chase the Joja company out of town by fixing the Community Center, Morris exclaims "I'm done for!" He might be completely literal about that.
While the shrine that erases your children's existence by turning them into doves is horrific enough, the fact that its owner is the Wizard's ex wife who is hinted to have left him after he cheated on her and had a child with another woman makes you wonder exactly why she owns it. Is she suspicious of her former husband? Or was the shrine the reason he left her in the first place?
The entire shrine and divorce system might be an extreme but effective way to subvert Permanently Missable Content in the game. Think about it: a player makes enough progress to have a thriving farm, perhaps collect most of the in-game achievements and rare items. They marry one of the candidates, which take in-game months to woo and propose to, but also want to see the heart events and married life with another candidate, hence the divorce. But they also don't want to permanently close off their relationship with the ex, so they basically Retcon the entire relationship out of existance.
Rabbits regularly drop rabbit's feet once you start raising them. That raises all kind of implications as to how they're being harvested.
Void Spirits AKA Shadow People are among the monsters you can kill for a reward in the Adventurer's Guild. Think about that for a second. The existence of Krobus pretty much confirms that Shadow People are sentient. Granted, Marlon and Gil probably just intend it to be in self-defense rather than actively seeking out and killing them, but still.
Stardew Valley is situated at the coast of the Gem Sea. The Gotoro Empire, which is at war with your country, is across the Gem Sea. Should the Gotoro Empire strike, Pelican Town and the rest of the valley would be subject to attack.
Less Fridge Horror, more Fridge Sadness. None of the characters have established ages, but Maru is old enough to be married and Sebastian is old enough that living in his parents' basement is a little embarrassing but young enough to be irritated by his mom coming to his room, and they both look fairly young. Sebastian would have been about ten years old at the most when Maru was born, probably younger. Demetrius has a book about how to be a first-time step dad but he never so much as mentions Sebastian's existence (or acknowledges your existence as his new son or daughter-in-law if you marry him). The situation is ambiguous, but given Demetrius' logical, scientific approach to pretty much everything in his life, it implies that his goal was "to be a dad", and he gave up on a less-than-ten-year-old Sebastian completely because he met that goal when Maru was born.
It may not be that, so much as that Sebastian's family likely doesn't quite "get" his interests (Robin is very much a rural, down-to-earth person, so may not quite grasp Seb's programming work or love of Fantasy, Demetrius is a practical and literal-minded man, which again would cause problems (programming doesn't produce tangible results like scientific study or engineering, and Fantasy stuff may be incomprehensible to him), and Maru isn't sure how to approach him since their personalities are polar opposites). There may have been considerable friction (either real or perceived) in the past when they tried to connect with him, and they've decided to just give him space.
Giving somebody space is one thing, being the black sheep of the family is one thing, but the only evidence in the entire game that Demetrius is even aware that Sebastian lives in his basement is that book. He doesn't acknowledge Sebastian's presence in the house, he doesn't react when Sebastian gets married and leaves home, and he doesn't acknowledge your relationship with him. I'd go as far as to say that Demetrius regards Sebastian as an Unperson in their home, except that would require Demetrius to at least admit that Sebastian lives in his house.
One of the objects you can build in your farm is a Fish Pond, which allows you to breed fish to gain eggs and a sustainable supply of those fish. After a while, those fish start giving you quests to help you boost the capacity of the pond, and they give you a general idea on how they're doing when you interact with it. In case you've missed the implications there... All those fish you've caught, cooked, sold and eaten raw? Yup, they're all sentient.
Alternatively, and slightly less horrifying, is that it's not actually the fish giving you quests, so much as that your character is able to interpret what they're wanting through the vague "forest magic" you're tapped into. (The same magic that lets you speak to bears and Junimos)
They are also still alive in your backback, fridge, or chest.
The sewer cave is generously littered with apparent human remains. Who are they? Ill-fated maintenance workers? Adventurous young people like Abigail and the kids? Financial liabilities for Joja?
The hospital is closed for a significant portion of each day, notably the night, when health emergencies are more likely to occur. Being the town's only doctor, Harvey is likely always on duty for such emergencies, even during his off times. The big Fridge Horror comes from the emergencies Harvey can't handle, like those requiring surgery, but he likely knows enough to stabilize those types of injuries just to give people enough time so they can be transported to a hospital. This is outright confirmed by any time you pass out from damage in the mines—you come to in the hospital, with a very worried Harvey hovering over you, having patched you up—and Shane's six-heart event: any time you find him, between 9 a.m. or 8 p.m., he'll end up in Harvey's clinic, where the doctor pumps his stomach and gets him some bed rest.
1.5 introduces a volcano with actual lava pools, which look more like actual lava (or at least a Coconut Effect version of lava) than the "lava pool" at level 100 of the mines, which is just water colored red. So what is up with the latter? Given that 99% of what you fish up there is literal garbage (which you'd think would burn up if it was tossed in actual lava), it's possible that it really is normal water, miscolored from insane amounts of pollution from all the litter. It would also explain why you only find one species of fish there, and even more rarely than you do fishing in the lava pools in the Volcano Dungeon; only the most robust species of fish can survive in that anymore, and even then they're not exactly thriving.