Hank: Nobody knows you like you know yourself, right? You know who you are, what you like, and what you're good at. You might know Voldemort’s seven horcruxes by heart, but you only memorized a list of amino acids for that one high school biology test, and forgot them right afterward.

No one knows everything, so you’d think people would be okay admitting that they don’t know something. But people generally aren’t so good at evaluating their own thinking, because of self-serving biases. Psychologists study lots of different biases, but self-serving biases can explain why you might believe that you know more than you actually do, or that your reasoning is better than it actually is.

So, one way to research self-serving biases in people is to ask if they know about completely made-up things. This can reveal a phenomenon called overclaiming, which is basically what it sounds like: when someone pretends that they know something, instead of admitting that they don't. For example, in one 2015 study, researchers asked people to rate their knowledge on a list of biology, philosophy, and literature topics.

Like, some biology terms were "mammal," or "adrenal gland." But secretly, there were some topics on the list that people couldn't have known anything about, because the researchers just made them up, like: "ultra-lipids," "bio-sexual," or "retroplex." And instead of admitting ignorance, 110 of the 124 people in the study claimed to know about or be familiar with one of these invented ideas. Not only that, but the more people said they knew about biology in general, the more likely they were to claim that they knew about fake biology terms. Now, it's possible that these results were because of honest mistakes — somebody read "ultra-lipids” and recognized the word "lipid," which is a real term for a fat or oil molecule.

Even though "ultra-lipids" aren't a thing. Or, it’s possible that the participants didn’t have real biology knowledge at all, but still thought they knew this stuff. So to figure out whether people with actual knowledge were still overclaiming, the researchers did a slightly different study involving personal finance topics.

Again, they asked participants about a list of specific topics, things like "inflation," and "Roth IRA,” and secretly mixed in some made-up topics. But this time, they paired this list with a personal finance quiz, to test actual knowledge. So instead of just checking a box saying you know what a Roth IRA is, you would have to answer questions to prove it — like whether or not it’s tax-deferred

And the researchers found that even people who actually knew more — who did better on the quiz — were also more likely to overclaim. They weren’t any better at picking out the fictional concepts, or admitting ignorance. Overclaiming can have some unfortunate consequences for people's real lives, too.

A national study of over 25,000 people found that the people who filed for bankruptcy at some point did horribly on that same written test of financial knowledge compared to those who hadn't — no real surprise there. But those people who struggled with financial knowledge were also more likely to give themselves the highest rating, when asked what they thought of their own knowledge.

This is an example of the “Dunning-Kruger” effect: when people who score really low on tests of knowledge or ability think they're doing really well. It’s something everyone is susceptible to, since everyone has different areas of knowledge, and lack of knowledge. This blind spot about our own thinking can make it hard for people to think critically about their own arguments, too.

Another team of psychologists demonstrated this by asking 237 people to solve five reasoning problems, and give arguments for their answers. Then, they had to judge someone else's argument for the same five problems, and they were given their own answers for comparison. But secretly, for one of the five problems, the researchers swapped the participant’s own argument for the stranger’s. The researchers hoped people wouldn’t recognize their own argument, and would judge it like a stranger’s. — that they were being asked to evaluate their own argument.

But of the 108 participants who didn't, 60 of them rejected their own arguments! And it wasn't just that they were being overly-critical of others. People were just plain better at finding flaws in their own reasoning when they thought it was someone else's.

This is called the bias blind spot: you can more easily see flaws in others' thinking, than recognizing flaws in your own. It's easy to hear about these psychology studies and conclude that people are dumb — but, thanks to self-serving biases, you can't expect everyone to always be aware of the gaps in their knowledge. That also means that you can go easier on yourself, too. These three words at the heart of all scientific inquiry: "I don't know."

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