Hearing or reading a statement more than once makes it feel more true, even when it’s false, an effect psychologists call the illusory truth effect. It happens largely because repeated statements are easier to process, and that ease feels like truth. For affirmations, it means repetition can make a line feel more familiar, but the effect is modest, it was found with trivia and headlines rather than beliefs about yourself, and repeating a line that clashes with how you see yourself can backfire.
What is the illusory truth effect?
The effect was first reported in 1977. Lynn Hasher and her colleagues showed people a list of plausible-sounding statements and asked them to rate how true each one was. Some were true, such as “Lithium is the lightest of all metals.” Some were false, such as “The capybara is the largest of the marsupials” (capybaras are rodents). In two later sessions, weeks apart, people rated a mix of statements they had seen before and new ones. With each session, they rated the repeated statements as more true, whether or not the statements actually were (Hasher, Goldstein & Toppino, 1977).
Since then the effect has been reproduced many times. A 2010 meta-analysis pooled 51 studies of it and found the effect was largest when repeated statements were compared with brand-new ones (Dechêne et al., 2010). Researchers have found it with trivia, product claims, opinion statements and rumors (Hassan & Barber, 2021), and with fake news headlines, where even a single earlier exposure made headlines seem more accurate, both in the same session and a week later (Pennycook, Cannon & Rand, 2018).
Why repetition feels like truth
The leading explanation is fluency. A statement you’ve met before is easier to read and understand the second time, and people treat that ease as a sign of truth. That shortcut usually serves us well, because most claims we come across are true, and in everyday life ease and truth tend to go together (Hassan & Barber, 2021; Brashier & Marsh, 2020).
Fluency doesn’t even need repetition. In one study, statements like “Osorno is in Chile” were judged true more often when printed in a color that was easy to read against the background than in one that was harder to read (Reber & Schwarz, 1999).
A useful way to think about it comes from a review of how people judge truth. We lean on three things: a default assumption that most claims are true, feelings such as how easy a statement is to process, and a check against what we already know. We can make that last check, but we don’t always do it (Brashier & Marsh, 2020). Researchers still debate the finer details, from simple familiarity to how a statement links up with things already in memory (Unkelbach et al., 2019).
How strong is the effect?
Strong enough to matter, modest in size, and with some limits.
- Knowing better doesn’t fully protect you. Repetition made false statements seem truer even for people who showed, on a later test, that they knew the right answer (Fazio et al., 2015).
- Plausibility matters less than you’d think. In a preregistered experiment, repetition increased belief across statements of every level of plausibility, with the largest effects for ambiguous ones (Fazio, Rand & Pennycook, 2019). In the fake-news study, though, repetition did nothing for completely implausible claims like “The earth is a perfect square” (Pennycook, Cannon & Rand, 2018).
- The shifts are modest. In a large registered study, repeated statements averaged 4.52 and new ones 4.14 on a scale from 1 (definitely false) to 7 (definitely true). That’s a real nudge, but less than half a point (Henderson, Simons & Barr, 2021).
- It fades with time. The same study found the effect immediately and after a day, a week and a month, but it shrank as the delay grew (Henderson, Simons & Barr, 2021).
- More repetitions bring diminishing returns. When statements were shown up to 27 times, perceived truth kept rising, but the biggest jump came from seeing a statement the second time, with smaller gains after that (Hassan & Barber, 2021).
- Checking helps. When people rated how accurate statements were the first time they saw them, the illusion disappeared later, but only for statements they knew something about (Brashier, Eliseev & Marsh, 2020).
This is why the effect gets so much attention in research on misinformation and advertising. A claim doesn’t have to be convincing to gain ground; it just has to be repeated.
Spotting it in everyday life
Once you know about the effect, you notice it everywhere: a slogan you’ve heard a hundred times, a rumor that keeps going around, a claim that “everyone knows.” Familiarity is not evidence. When something feels obviously true, it’s worth asking a second question: do I know this, or have I just heard it a lot? Asking about accuracy the first time you meet a claim is one habit shown to blunt the effect, at least when you know something about the topic (Brashier, Eliseev & Marsh, 2020).
What it means for affirmations
It’s tempting to read all this as proof that affirmations work: say something enough times and you’ll believe it. The research supports a smaller claim.
What it does support:
- Repetition makes lines familiar. Familiar statements are easier to process and a little easier to accept. That’s a fair argument for repeating a good line rather than reading it once.
- You don’t need hundreds of repetitions. In the studies, the second exposure did the most, and the effect faded over weeks. Coming back to a line on different days makes more sense than saying it 50 times in one sitting.
What it doesn’t support:
- It hasn’t been tested on beliefs about yourself. The studies use statements about the world, like trivia, headlines and product claims, rated on a scale. Beliefs about your own worth or ability are tied up with memories, feelings and daily evidence, and there’s no good reason to assume they move the same way.
- The closest direct test went badly. When people with low self-esteem repeated “I’m a lovable person,” they ended up feeling worse, not better (Wood, Perunovic & Lee, 2009).
- You fact-check affirmations without trying. When you say a line about yourself, you compare it with what you know about your life. In the accuracy study above, checking a claim at first exposure removed the illusion when people had relevant knowledge. It seems likely, though it hasn’t been tested, that a line you instantly dispute gets little help from repetition.
The practical upshot: repetition is most useful for lines that are already plausible to you. “I’m learning to speak up in meetings” can feel more natural each time you say it. “I am a fearless leader” mostly gives your inner critic another chance to argue.
The same mechanism may work against you, too. Nobody has tested it directly with self-talk, but if repetition makes statements feel truer, the harsh lines you repeat to yourself (“I always mess things up”) could be getting the same boost. Noticing and answering them matters as much as adding new lines, and our guide to stopping negative self-talk shows how.
In practice
- Choose lines you can already half-believe. True today, or true as work in progress: “I’m learning to…”, “I can…”.
- Repeat them a few times, on more than one day, rather than many times at once.
- Give them a reason. “I can handle this deadline, because I handled the last one” gives your memory something to agree with.
- Answer the old lines. When a harsh thought repeats, reply with a fairer one, every time.
- Use your own words, so the line sounds like something you would actually say. Our affirmations for confidence are written to pass that test.
The short version
- Repetition makes statements feel truer, even false ones. This illusory truth effect has been reproduced many times since 1977.
- It works mainly through fluency: repeated statements are easier to process, and ease feels like truth.
- The effect is modest and fades, and most of it comes from the first repeat.
- It hasn’t been shown to change beliefs about yourself. Repeat lines you can already believe, and don’t expect repetition to make an unbelievable one stick.