Ten Wrong Things We “Just Know”

We only use 10% of our brains

One of the most persistent, and yet most stupid of all these things “we all know” – as if evolution wouldn’t have trimmed away the 90% of useless matter from an organ that takes 20% of all our energy just to run. Brain imaging technology, particularly fMRI, shows that virtually every region of the brain is active at some point throughout the day — and most are active nearly all the time, even during sleep. No neurologist has ever identified a dormant 90%. The myth likely arose from a series of misunderstandings, starting right back with the first early neuroscientists, who found that poking "motor cortex" cells with electricity caused muscles to twitch, but poking other large areas of the brain did nothing so obvious (which people assumed meant “nothing”).

Lightning never strikes the same place twice

Tell that to Roy Sullivan, a U.S. Park Ranger in Virginia who was struck at least seven times. Lightning strikes the same places repeatedly — tall structures practically depend on it. The Empire State Building is struck roughly 20–25 times per year. Lightning rods work precisely because they attract repeated strikes. Physics doesn't care about metaphors: lightning seeks the path of least resistance, and that path doesn't change between storms. Some scientists have even suggested that up to a third of lightning strikes are on spots already struck.

You swallow several 8 spiders a year in your sleep

This one is particularly funny, because it was invented on purpose – to show how quickly nonsense spreads. In 1993, a columnist fabricated it as an example of ridiculous misinformation people accept uncritically, and when the internet came along it soon became one of the internet's most-shared facts. In reality, spiders avoid sleeping humans: the vibrations, breathing, and body heat register as threats. It essentially never happens.

Goldfish have a 3-second memory

Goldfish can form and retain memories for months. They have been trained in laboratories to press levers for food at specific times of day, navigate complex mazes, and recognise familiar humans. The myth is thought to originate from the fact that goldfish bowls are small and repetitive — people assumed a dull environment meant a dull mind. (Granted, if you send one out for the shopping it will never return with the milk.)

The Great Wall of China is visible from space

The Wall is extraordinarily long but only 15–30 feet wide — far too narrow for the naked eye to resolve from low Earth orbit, let alone the Moon. It’s been compared to seeing a human hair from two miles away. Multiple astronauts have confirmed they cannot see it. Even from low orbit, you'd need optical aids. By day, very few manmade structures are visible, and they tend to be either vast agricultural areas (like the 64,000-acres of the Greenhouses of Almería in Spain), or structures like the Palm Jumeirah in Dubai, which has a very distinct shape and contrasts with the dark water around it. The whole myth predates spaceflight entirely.

Humans have only five senses

The "five senses" framework is ancient philosophy, not science. Humans have numerous additional senses including proprioception (awareness of body position), thermoception (temperature), and the vestibular sense (balance and spatial orientation). These are just examples – depending on how they categorise them, neuroscientists count up to 21 distinct senses.

Sugar makes children hyperactive

It seems obvious, but apparently it’s not true. Over a dozen double-blind, placebo-controlled studies have found absolutely no link between sugar consumption and hyperactivity in children. The effect is entirely expectation-driven: sugary drinks are served at parties, or parents told their child consumed sugar rated their behaviour as more hyperactive, even when the child had been given a sugar-free drink. It is a textbook case of confirmation bias in everyday life.

Carrots improve your eyesight

Carrots won't sharpen normal, healthy eyesight. The myth was deliberately manufactured by British wartime propaganda in WWII: the RAF was secretly using radar to locate enemy aircraft, but they didn’t want the Germans to know that. So they told the press their pilots ate lots of carrots. The story stuck, got absorbed into public health advice. (Of course they do contain beta-carotene, which may help if you are already significantly Vitamin A deficient - but this is rare in a population with a reasonably balanced diet, and quite accidental to the claim’s origins.)

When Columbus sailed for America, everyone thought the world was flat

Not at all. As far back as the third century BCE, Aristotle declared with certainty that the Earth was spherical. And though it might’ve taken a wee while for everyone to agree, Christopher Columbus himself, and the people involved in the expedition, knew Earth was a sphere. According to historian Jeffrey Burton Russell, “with extraordinary few exceptions no educated person in the history of Western Civilization from the third century B.C. onward believed that the Earth was flat.” That might have been before the internet, mind you.

Going out with wet hair will cause illness

Water is just water. Colds are caused by a virus, and they don’t care whether your hair is wet or dry. You cannot catch a cold or the flu simply from going out with wet hair, even during winter: you either have the virus or you don’t.  There is, in fairness, something called Temperature Stress: if being wet causes your core body temperature to drop, it can possibly make it slightly harder for your immune system to fight off viruses that were already in your system. But even if that’s all true, it can’t cause the virus.