50 things I learned in 2025

January 10, 2026

Second year of documenting one TIL each week! (Here’s 2024)

Blueprints are blue because of the cyanotype process invented in 1842 by John Herschel. The process used photosensitive chemicals (ammonium iron citrate and potassium ferrocyanide) that turned Prussian blue when exposed to light. You’d place a translucent drawing over chemically-coated paper, shine bright light on both, and wherever the drawing’s lines blocked the light, the paper stayed white, creating white lines on a blue background. (Why Are Blueprints Blue?)
Lobsters aren’t actually immortal, they just age differently. They produce telomerase indefinitely and don’t weaken with age like mammals do, but they keep growing, which means they keep molting, and eventually that process becomes so energy intensive that it kills them. (Don’t Listen to the Buzz: Lobsters Aren’t Actually Immortal)
Carrots don’t actually improve our eyesight. They contain vitamin A which prevents night blindness if you’re deficient, but if your eyes already work fine, eating more carrots won’t sharpen your vision. Didn’t stop my family from nagging me to eat them as a kid though. (Do carrots really help you see in the dark?)
French sports retailer Decathlon started as a wholesaler selling Nike and Adidas before creating any of its own gear. They didn’t launch their first in-house brand Quechua until 1997, over 20 years after it was founded.
Credit cards with rotating 5% cash back categories require people to activate them each quarter because sludge (intentional friction, the opposite of nudge) benefits the company. They advertise the full reward to get people to sign up, but the activation requirement filters out forgetful customers who subsidize the program by spending without getting the bonus.
Superscript numbers on EU menus are due to a 2014 regulation requiring allergen disclosure on all food, including restaurant dishes. The US requires allergen info on packaged foods, but most restaurants aren’t required to disclose allergens on menus at all, so you mostly have to rely on your server. (Food information to consumers - legislation)
Brunch was invented by a hungover British writer in 1895 who wanted a lighter Sunday meal that let people who got drunk on Saturday night sleep in. It didn’t become a cultural phenomenon until post-WWII America, when women entering the workforce pushed families to eat out on Sundays instead of cooking elaborate meals at home.
Fizzy drinks don’t help digest greasy food. The relief we feel after drinking Coke or Pepsi with a heavy meal is from releasing gas, not actual digestion. Carbonation can even worsen acid reflux and adds more gas to the stomach. Fast food chains keep pairing sodas with greasy food because fountain drinks cost pennies to make and sell for dollars, so profit margins are massive (90%). The more we associate that satisfying burp with digestive relief, the more they profit. (Carbonated beverages and gastrointestinal system: Between myth and reality)
There’s a real medical term for why we pass gas more on airplanes: high altitude flatus expulsion (HAFE). Airplane cabins are pressurized to 6,000–8,000 feet, so the gas in our intestines expands by about 25–30% mid-flight according to Boyle’s Law. It’s the same reason chip bags puff up during flight. So it’s merely physics, not poor manners.
Ceviche, one of my favorites, turns out to be a fusion dish. Ancient Peruvians used fermented passionfruit juice to preserve fish. Then Spanish colonizers brought citrus in the 1500s, and the lime marinade replaced the original method entirely. (Ceviche: the surprising history behind Peru’s raw fish dish)
Pacific salmon become zombies after spawning. They stop eating, burn through all their reserves, and their bodies literally rot alive while they’re still swimming, skin falling off, eyes going cloudy or even missing sometimes, fungal infections spreading. Their rotting bodies release marine nutrients that feed everything in the river, including the next generation of salmon. (Zombie Salmon)
In the Netherlands, Belgium, and much of Northern Europe, toilets are separated from bathrooms for practical reasons: hygiene and letting multiple people use facilities at once. Japan separates them too, but for completely different cultural reasons: the toilet is considered “unclean” and gets its own room (often with dedicated slippers), while the bath is sacred space for relaxation. (The Dutch toilet: Everything you need to know before you go, Japanese Bathrooms: Why are they Different?)
About 20 Japanese tourists a year develop Paris syndrome, psychiatric symptoms severe enough to need hospitalization because Paris doesn’t match the idealized fantasy sold by Japanese media. Turns out marketing a city as a pristine romantic dream, then sending people from one of the world’s most polite cultures into actual Parisian service culture, creates a collision brutal enough to cause hallucinations and delusions.
In Japanese folklore, household objects like umbrellas, sandals, and tea kettles that reach 100 years gain consciousness and become tsukumogami: conscious spirits that are mostly harmless, but become vengeful if thrown away carelessly. It’s folklore’s way of teaching respect for our belongings and the tools that serve us.
The thorny devil lizard drinks water with its feet. Their entire skin is covered in microscopic grooves that channel moisture straight to their mouth via capillary action. (Australia’s thorny devils drink water by burying themselves in sand)
Research shows that when people feel nostalgic, they value money less and are willing to pay more for products. The mechanism: nostalgia makes us feel socially connected, and when we feel connected to people, we care less about money, which ironically makes us more willing to spend it. (Nostalgia Weakens the Desire for Money)
Clever Hans, a horse who appeared to do math in the early 1900s, was actually just reading his handler’s unconscious body language cues. The Clever Hans Effect now describes any time a subject appears to understand something but is just picking up on unintended signals. (Clever Hans)
The Zeigarnik effect explains why unfinished tasks occupy mental space even when we’re not actively working on them. Psychologist Bluma Zeigarnik observed that waiters could recall complex unpaid orders but immediately forgot them after payment. Our brains treat incomplete work as open loops demanding attention and only release that cognitive tension when the task is finished. (Zeigarnik Effect)
World Sleep Day exists. It’s the Friday before the spring equinox every March and is an awareness campaign by sleep researchers since 2008, not something people actually participate in. (Though nothing stops you, of course.)
The word “dating” didn’t exist until 1896. A Chicago columnist coined it when describing someone whose girlfriend was “fillin’ all my dates” as in the dates on her calendar.
Marriage counseling was institutionalized by American eugenicists in the 1930s as the “positive” side of eugenics. These people also spent years advocating for forced sterilization, but pivoted to promoting “fit” marriages when the optics got bad. (The Surprising History of Marriage Counseling)
Originally, signet rings were people’s legal signature. People pressed them into hot wax to seal documents, with the design carved in reverse so the impression would show correctly. Breaking someone’s seal was basically identity theft.
Sichuan peppers aren’t actually peppers. They are dried berry husks of berries from a tree that belongs to the citrus family, and they numb rather than burn.
We all have invisible zebra stripes called Blaschko’s lines, and they map the migration paths of our skin cells during fetal development: V-shapes on the back, S-curves on the torso, waves on the limbs. Most of us never see them, but people with certain genetic mutations or skin conditions can watch these embryonic blueprints light up across their skin. (Humans Actually Have Secret Stripes And Other Strange Markings)
Escher sentences look grammatically fine until you realize they mean nothing at all, like “More people have been to Russia than I have.” The brain fills in the blanks because it assumes the sentence must make sense, but the comparison doesn’t actually work.
The Fermi paradox is the contradiction between how likely alien life should exist and the complete absence of evidence we’ve found. Given how old and vast the universe is, we should have detected something by now, but we have not. We still don’t know if it’s because intelligent life is extremely rare, civilizations destroy themselves before going interstellar, or we’re just listening wrong.
A mondegreen is when you mishear lyrics and substitute similar-sounding words that create a different meaning. Writer Sylvia Wright coined the term in 1954 after mishearing “laid him on the green” as “Lady Mondegreen” in a Scottish ballad. The term itself is a mondegreen.
Dwarf lemurs from Madagascar lengthen their telomeres during hibernation, temporarily reversing cellular aging. They’re the only hibernators known to do this. The effect does disappear within two weeks after waking up. (Hibernating Lemurs Can Turn Back the Clock on Cellular Aging)
When we hear something enough times, two things happen: we start to like it (mere exposure effect) and we start to believe it’s true (illusory truth effect) even when we initially knew it wasn’t. Our brains mistake familiarity for both preference and accuracy.
Unlike most marsupials, wombats have backward-facing pouches to keep dirt out and their joey clean and protected as they spend their lives burrowing. (Wombat Fact Sheet)
Fortune cookies were invented in California by Japanese immigrants in the early 1900s. They only became “Chinese” after WWII, when Chinese bakeries filled the production gap and the association just stuck. China doesn’t serve fortune cookies, locals think they are a weird American thing. (The Surprising Origins of the Fortune Cookie)
The Q-tip box literally says “do not insert into ear canal” but the product design suggests that’s exactly what it’s for. 96% of people use them to clean their ears anyway. Meanwhile, ears clean themselves through jaw movements like chewing and talking. (Ear-Rational Behavior: A Survey Study of Q-tip Cotton Swab Habits and Health Perceptions)
When you have a room of 23 people, there’s a 50% chance that two of them share a birthday. This is the birthday paradox.
Laser is an acronym. So is taser, scuba, and radar.
North Sentinel Island is home to the Sentinelese, one of Earth’s last uncontacted peoples. They’ve violently rejected all contact for centuries. India legally bans anyone from approaching within 5 km. We don’t know their language, their population, or what they call themselves.
Anchoring effect and contrast effect often work together to warp our judgment. We see a $500 jacket first, then $200 one feels reasonable (anchoring). But if we see that $200 jacket next to a $50 one, then it suddenly feels expensive (contrast). The first number we see shapes expectations, and the comparison magnifies differences.
Birds practice anting where they deliberately rub ants through their feathers or let them crawl all over their bodies. Leading theories for why they behave this way include parasite control, feather maintenance, and merely seeking the sensation of formic acid (birds will substitute cigarette butts and mothballs when ants aren’t available).
The buttered cat paradox combines two “laws”: cats always land on their feet (real biomechanical reflex) and toast always lands butter down (Murphy’s Law). The joke goes: strap them together and drop them, they’d hover forever.
All my life, I had thought you were supposed to spit out the seeds when eating pomegranates. Turns out pomegranate seeds are actually arils (juice sacs with seeds inside) and the whole thing is edible. (Are Pomegranate Seeds Safe to Eat?)
The Barnum effect is why horoscope feels weirdly accurate. We’re really good at filling in the blanks with our own specifics and mistake vague, flattering statements for real insight about ourselves.
Thanks to the Jevons paradox, the more efficient we become in anything, the more work we do. Efficiency doesn’t reduce workload, it expands what we think is possible, so we take on more.
While zebras and horses look similar, the former are vicious, aggressive and lack the temperament and social structure that the latter had when they were domesticated around 5,500 years ago, hence we ride horses and not zebras. (The Story Of... Zebra and the Puzzle of African Animals)
In billiards, skilled players don’t just sink balls. They position the cue ball after each shot to set up the next one. Reputation works the same way. Each time you follow through, you make the next opportunity easier. But one major breach can undo all of it, because trust is harder to rebuild than it is to maintain. (The Reputational Cue Ball)
Vinyl records store music as a physical shape. The groove carved into the disc is a literal snapshot of sound waves. When a record plays, a needle rides through those microscopic wiggles and vibrates the exact same way the original music did, translating bumps back into sound. (The great mystery of vinyl)
Western Union started as a telegraph company in 1851. They started offering money orders in 1871 as a side service since they already had a nationwide network of offices, and by 2006 money transfers became their whole business. (Western Union Corporation)
The movie Zootopia has three different titles (US got Zootopia, the UK and Denmark got Zootropolis, and Germany got Zoomania) because each name change came down to trademark conflicts in that specific market. A Danish zoo owned Zootopia for merchandise. A German children’s book already used Zootopolis which sounds too close to Zootropolis.
Apple’s laptop sleep light pulses at 12 breaths per minute, matching human respiratory rates during rest, because they patented the “breathing” effect after researching what would feel psychologically calming. (Breathing status LED indicator)
The Matthew effect explains that initial advantages create feedback loops where success breeds more success. Kids who read well early read more and get better. Famous scientists get more credit even for comparable work. The rich literally get richer.
Inside an igloo, snow keeps us warm because air trapped between ice crystals makes it an excellent insulator. Body heat alone can create a 60-degree temperature difference between inside and out. The terraced floor design helps too, as cold air sinks to the entrance level while warm air rises to where you sleep.
In English, people say “close to my heart.” In Chinese and Vietnamese, the metaphor stacks vital organs to intensify closeness, so people say “heart and liver” (心肝), which means my darling, my irreplaceable person.