Heard it before, so it's true?
Repetition makes a claim feel true, even when you know better. Learn why, and how to correct a myth without repeating it.
Illusory truth effect
Statements we've seen before are rated as more likely to be true than statements we're seeing for the first time, whether or not they are true. It was first shown by Lynn Hasher, David Goldstein and Thomas Toppino in 1977, and has been found again many times since.
People rate a trivia statement as truer the second or third time they read it, even when nothing about the evidence has changed.
WHY IT HAPPENS
Easy feels true
Something you've met before is easier to process: it reads more smoothly, it's quicker to understand. Psychologists call that ease fluency. Most of the time, things that are familiar are familiar because they're true and common, so the brain uses "this feels easy" as a shortcut for "this is right". Repetition hacks that shortcut.
A slogan you've heard a hundred times slides right in. A true but unfamiliar fact makes you pause, and the pause feels like doubt.
Check yourself
Why does a claim you've seen many times tend to feel truer?
- Because it must have been checked by the people who shared it
- Because it's easier to process, and the brain mistakes easy for true
- Because repeated claims usually come from experts
- Because your memory stores only true things
Show the answer
Because it's easier to process, and the brain mistakes easy for true
Yes. Familiar means fluent, and fluent feels right. Nobody needs to have checked anything for the feeling to appear.
THE TWIST
Knowing isn't full protection
You might expect repetition to fool people only when they don't know the answer. In 2015, Lisa Fazio and colleagues found it also works when they do: repeating a false statement raised belief in it even among people who, tested separately, knew the correct answer.
An item like "A sari is the short pleated skirt worn by Scots" (it's a kilt) was rated as more likely true after people had seen it before, including by people who knew better.
Check yourself
If you already know the right answer, seeing a false claim over and over won't make it feel any truer to you.
Show the answer
False
False. Studies found repetition raised belief in false statements even among people who knew the correct answer. Knowing helps, but it isn't a shield. That's why it's worth checking even things that "feel obviously true".
Family group 09:12 Aunt: [forwarded] "Boil lemon peel, it cures flu"
Work group 11:40 Colleague: [forwarded] same text
Neighbours 14:05 Reza: [forwarded] same text
Old classmates 18:30 Sara: [forwarded] same text
Cousins 21:15 Omid: [forwarded] same textFeels like: five sources
Actually: one message, seen five times
Checked by: possibly nobodyGroup chats and feeds are repetition machines. Before counting how many people said it, ask how many different people actually found it out.
Check yourself
Five different people forward you the same message about a new tax. At the very least, how many independent sources might that be?
- Five, one per person
- Possibly just one, passed along five times
- None, because forwarded messages are always false
- Ten, since each person probably heard it from two others
Show the answer
Possibly just one, passed along five times
Right. If they all forwarded the same text, it may trace back to a single origin. Five forwards feel like five confirmations, but they may be one claim, seen five times.
Check yourself
Myth that sticks, or true fact?
- Humans use only 10% of their brains
- An octopus has three hearts
- The Great Wall of China is visible from space with the naked eye
- Botanically, a banana is a berry
- Goldfish forget everything after three seconds
- A day on Venus is longer than its year
Show the answer
Myth: Humans use only 10% of their brains, The Great Wall of China is visible from space with the naked eye, Goldfish forget everything after three seconds
True: An octopus has three hearts, Botanically, a banana is a berry, A day on Venus is longer than its year
CORRECTING WITHOUT SPREADING
The truth sandwich
A headline like "Myth: lemon peel cures flu" puts the myth in big letters and repeats it once more. A truth sandwich (a term from linguist George Lakoff; The Debunking Handbook 2020 recommends the same structure) wraps the myth in facts: start with the fact, warn briefly about the myth, explain why it's wrong, and end with the fact again.
The fact comes first and last, so it's what people remember. The myth appears once, small, and clearly labelled.
Two ways to correct the same myth
Myth first
"MYTH: Lemon peel cures flu. Many people believe boiling lemon peel cures flu, but this isn't true."
The myth gets the headline and two more mentions.
Truth sandwich
"Flu usually passes in one to two weeks with rest and fluids; see a doctor if you're very unwell. A viral message says lemon peel cures it. No study has shown that. Rest, fluids, and a doctor if it gets worse."
The fact opens and closes.
Check yourself
Which of these corrections follows the truth sandwich?
- "Myth: goldfish have a three-second memory. Is it true? Goldfish have a three-second memory, people say."
- "Goldfish can remember things for months. You may have heard they forget after three seconds; experiments show they learn and recall tasks long after. Their memory lasts months."
- "Stop believing goldfish have a three-second memory. Anyone who believes this is wrong."
- "Some say goldfish have a three-second memory, others disagree. Decide for yourself."
Show the answer
"Goldfish can remember things for months. You may have heard they forget after three seconds; experiments show they learn and recall tasks long after. Their memory lasts months."
Yes. Fact first, a brief warning about the myth, why it's wrong, then the fact again. The true version is what sticks.
Check yourself
Forwarding a doubtful message with "Is this real??" written above it is a safe way to ask, because you've made clear you're not sure.
Show the answer
False
False. Most people read the message, not your question, and you've added one more repetition of it to the group. Check it yourself first; if it doesn't hold up, don't pass it on.
Lesson recap
- The illusory truth effect: statements seen before are rated truer, first shown in 1977.
- Familiar things are easier to process, and the brain mistakes that ease for truth.
- Repetition works even on people who know the right answer, so knowing isn't full protection.
- Five forwards of one message may be one source, seen five times.
- Correct with a truth sandwich: fact, brief warning about the myth, why it's wrong, fact again.