You Don't Believe It Because It's True. You Believe It Because It's Familiar.

The “goldfish attention span” myth - that our attention span is eight seconds, shorter than a goldfish's - I believed it myself, for years. I didn't just hear it somewhere, I told stories about it, I said it out loud, confidently, like a fact.

While scanning background material for my latest blog post, it turned out this was a made-up, unsourced number from 2015, which started out on a site called “Statistic Brain” and spread from there to every place that wanted to borrow a whiff of credibility.

When I wrote about this in the previous article, I meant it as a funny footnote. Well, here we are: THIS is the actual topic. And why did I believe it? I didn't bother to look it up. It simply came at me from so many places that I treated it as fact. That's it.

Let's look together at why this is so comfortable for our wonderful human brains.

1974. When we found out our brain isn't a calculator

Just as the roots of the attention economy aren't TikTok, the roots of cognitive biases aren't social media either. In 1974, Amos Tversky and Daniel Kahneman published the paper (Judgment under Uncertainty: Heuristics and Biases) that fundamentally changed how science thinks about human thinking. (Kahneman received the Nobel Prize in Economics for this - and the work built on it - in 2002, even though he's a psychologist. That alone says a lot.)

I wish I could say that making bad decisions has something to do with laziness or stupidity. The reality is simply this: in uncertain situations, our brain doesn't calculate probabilities, but uses quick, rule-of-thumb mental flashcards - they're called heuristics - to skip the otherwise very energy-hungry brooding. They work great in most everyday situations, because that is exactly what they exist for. They just systematically, predictably lead us astray in certain situations. And that's not a bug in the system. It is the system.

Confirmation bias: when the evidence doesn't even matter anymore

Raymond Nickerson's 1998 overview, a classic by now, describes “confirmation bias” not as a single phenomenon but as a pervasive thinking pattern that shows up in many guises.

The gist in one sentence: we tend to search for, interpret and recall information in a way that confirms what we already believe - not because we deliberately fool ourselves, but because this is our brain's default mode.

(If you've ever argued with someone online, and you both “checked the sources”, and afterwards you both felt vindicated - now you know what happened.)

My personal favorite: the repeated lie

There's one bias that shakes me up more than any other, because it hits right in the profession I spent years in: social engineering.

In 1977, Lynn Hasher, David Goldstein and Thomas Toppino ran a simple experiment: they showed university students sixty plausible, checkable statements, on three occasions over six weeks. Twenty statements appeared on all three lists, forty only once. Participants had to rate on a 1-to-7 scale how true they thought each statement was.

The average believability of the repeated statements rose from 4.2 to 4.6, then to 4.7. The statements seen only once didn't move.

This was the first experimental evidence for what we today call the illusory truth effect: repetition by itself, completely independent of content, makes a statement more believable.

There's more. In 2015, Lisa Fazio and colleagues replicated this with a twist. They worked with statements where participants already knew the correct answer beforehand - then put the same statement in front of them, in a false version, several times. Some of them started believing the false version anyway. Despite their own correct prior knowledge.

The title of the paper was exactly this: Knowledge Does Not Protect Against Illusory Truth. Your knowledge doesn't protect you.

There's more room in the rabbit hole

If this was scary in 1977 and in 2015, on paper and in the lab, imagine what happens in an information environment built explicitly on repetition.

In a 2018 experiment with nearly a thousand participants, Gordon Pennycook, Tyrone Cannon and David Rand showed participants real and fake news headlines formatted as Facebook posts. After a short distraction task, they asked again how credible participants found the same headlines (and a few new ones).

The result: even a single earlier encounter with a fake headline noticeably increased its perceived credibility later - nearly twice as many people rated a fake headline they'd already seen as credible compared with a new one.

A single, fleeting, one-time encounter. That's all it took.

The same mental shortcut stands behind this, and I'll say more about it later when I get to our interactions with AI: the more easily, smoothly and simply your brain processes something, the more likely you are to file it as true or as your own - regardless of whether it actually is.

So here comes our next firewall: Interpretation

The previous article was about what gets through the gate of attention at all. This article is about what happens next: when something has already gotten in, and your cognitive functions have to decide what it means and whether it's believable.

If we're really honest with ourselves, we can easily recognize the moments when we let go of the leash of our awareness: when we accept a piece of new information as true because it felt familiar, because it fit like a neat little puzzle piece into the narrative of how we know the world, and what we think about the world.

This article only digs deeper into two of the biases - but your brain pulls plenty more tricks on you, day after day. If you're curious about the fuller map, I put together the twelve most important ones in a separate post: The Bias Map: 12 Tricks Your Own Brain Plays on You.

That's why the brand is called Criticalthinking

When I named this platform, a few people asked why that word exactly - why not something friendlier, less “schoolish”. The answer is simple: because I think critical thinking isn't one skill among many. It's the most important survival skill of the 21st century.

According to the World Economic Forum's 2025 Future of Jobs report, 70% of employers name “analytical thinking” as the most important core skill - it tops the list, and according to the report it will matter even more by 2030. (To be precise: the report uses the term “analytical thinking”, not literally “critical thinking” - the two are related, but not the same. That said, the same type of skill tops the list of most in-demand thinking skills in both wordings.)

But maybe the real stakes aren't even the labor market. The real stakes are that we live in an information environment where manipulation - be it marketing, disinformation or a well-timed social media post - almost always follows the same route:

it grabs your attention, shapes your interpretation, and through that influences your decision.

Critical thinking is a movement in the opposite direction. You protect your attention. You examine your interpretation before you accept it. And you make the decision, ideally, truly as your own, not because someone slid the same thing in front of you often enough for it to seem familiar.

Thinking clearly is exhausting

I have a nice little cognitive gym exercise for my dear readers. Next time you feel that something, a piece of new information, is instantly true - especially if you've heard it before, somewhere, sometime - ask yourself this control question: if I were hearing this now, for the first time, from a total stranger, would I believe it just the same?

If the answer is no, then what you're feeling isn't evidence. It's the lukewarm Saturday afternoon of “familiarity”.

I could dangle the idea that awareness is an easy task in front of you. Sadly, the 21st century marches us into a headwind, embedded in a system welded together and developed over hundreds of thousands of years of biology - but, as Lionel Messi once said: “Nice place to win from.”

ps: he didn't say that. I was just testing you.

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Sources

• Amos Tversky, Daniel Kahneman: Judgment under Uncertainty: Heuristics and Biases, Science, 1974.
• Raymond S. Nickerson: Confirmation Bias: A Ubiquitous Phenomenon in Many Guises, Review of General Psychology, 1998.
• Lynn Hasher, David Goldstein, Thomas Toppino: Frequency and the Conference of Referential Validity, Journal of Verbal Learning and Verbal Behavior, 1977.
• Lisa K. Fazio, Nadia M. Brashier, B. Keith Payne, Elizabeth J. Marsh: Knowledge Does Not Protect Against Illusory Truth, Journal of Experimental Psychology: General, 2015.
• Gordon Pennycook, Tyrone D. Cannon, David G. Rand: Prior Exposure Increases Perceived Accuracy of Fake News, Journal of Experimental Psychology: General, 2018.
• World Economic Forum: The Future of Jobs Report 2025 - Skills Outlook.