Heuristics and Errors in Judgment

Dr. Esther Hattingh

Welcome back to Thinking Fast and Slow. I’m Dr. Esther Hattingh, and today we’re diving into some of the most quietly powerful forces shaping our decisions—those little mental shortcuts that Kahneman calls heuristics. Now, if you’ve been following along, you’ll remember in our last episode we talked about how System 1, our fast, intuitive mind, loves to jump to conclusions. Well, today’s first topic is a perfect example of that: the law of small numbers.

Dr. Esther Hattingh

So, what is this law of small numbers? It’s not a real law, actually—it’s more of a running joke between Kahneman and Tversky. The idea is that our minds, especially System 1, tend to trust results from small samples way too much. We see a handful of coin flips—say, four in a row—and if they all come up heads, we start thinking, “Wow, maybe this coin is special!” But statistically, small samples are just more likely to give us extreme results. It’s like, I always mix up the math, but if you flip a coin a thousand times, you’ll get close to fifty-fifty. But with just four flips? Anything can happen.

Dr. Esther Hattingh

This isn’t just a quirky thing about coins, though. It shows up everywhere. In research, for example, people—sometimes even professionals—design studies with tiny sample sizes and then get excited about dramatic findings. But those results are often just noise. This is a big reason behind what’s called the replication crisis, especially in psychology and medicine. We see a flashy result in a small study, but when someone tries to repeat it with a bigger group, poof, the effect disappears.

Dr. Esther Hattingh

I’ll tell you, I’ve fallen for this myself. Early in my career, I ran a student survey—just a small group, maybe twenty or so. The results were all over the place, but I was so eager to find patterns that I started drawing big conclusions. Later, with a larger sample, those patterns just melted away. It was a humbling lesson in how our minds crave stories, even when the data is just random noise. So, if you ever find yourself wowed by a dramatic statistic from a tiny group, just pause and ask: is this really meaningful, or is it just the law of small numbers at work?

Dr. Esther Hattingh

Now, let’s shift gears a bit—though, honestly, it’s all connected. Another way our minds get tripped up is through something called the anchoring effect. This is one of Kahneman and Tversky’s most famous discoveries. Basically, if you’re exposed to a number—even a totally random one—it can sway your estimate of something completely unrelated. Like, if I ask, “Was Gandhi older or younger than 144 when he died?”—which, I mean, obviously, he wasn’t 144!—but just hearing that big number makes people guess higher than if I’d said, “Was he older or younger than 35?”

Dr. Esther Hattingh

It’s wild, right? And it’s not just trivia. This anchor-and-adjust heuristic pops up everywhere. Think about financial decisions—how much to save for retirement, or what salary to ask for in a new job. If you start with a high anchor, you’ll probably end up negotiating for more. Even in everyday life, like shopping, those “suggested retail prices” are anchors. They set a reference point, and we adjust from there, but never quite enough.

Dr. Esther Hattingh

I actually used this in my own work, designing donation forms for a university fundraising campaign. We found that if we suggested higher donation amounts as starting points, people tended to give more—even if they could choose any amount they wanted. It’s not manipulation, exactly, but it’s a reminder of how easily our minds latch onto the first number we see. So next time you’re filling out a form or haggling over a price, just notice what anchors are being set for you. Sometimes, just being aware of the anchor can help you adjust a bit more thoughtfully.

Dr. Esther Hattingh

And speaking of what’s top of mind, let’s talk about the availability heuristic. This one is all about how easily something comes to mind, and how that shapes our sense of how common or likely it is. If you can quickly think of examples, you’ll probably think it happens a lot—even if that’s not true.

Dr. Esther Hattingh

The classic example is household chores. If you ask couples to estimate what percentage of the chores they do, their answers almost always add up to more than 100%. Why? Because it’s so much easier to remember the times you did the dishes than the times your partner did. Or, think about media coverage of rare diseases. If a disease gets a lot of attention, people start to overestimate how common or dangerous it is. Same with spiders—everyone knows about black widows and brown recluses, so we overestimate the risk, even though most spiders are harmless.

Dr. Esther Hattingh

I remember a few years ago, there was a big international news story here in South Africa—something dramatic, I won’t get into the details. The next semester, my students were suddenly much more anxious about that particular risk, even though statistically, nothing had changed. It was just more available in their minds. That’s the power of availability: it shapes our fears, our priorities, even our arguments about who does the laundry.

Dr. Esther Hattingh

So, as we wrap up, just remember—our minds are brilliant, but they’re also full of shortcuts that can lead us astray. Whether it’s trusting small samples, getting anchored by random numbers, or letting vivid memories shape our sense of reality, these heuristics are always at work. Next time, we’ll dig even deeper into how we can spot these patterns and maybe, just maybe, outsmart them. Until then, keep thinking—fast and slow.