Shankar VedantamHost, Hidden Brain · Journalist, Writer, Science Correspondent

You Don't Understand How a Toilet Works

3 Jul 2026 · 1 min

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In this brief Hidden Brain segment, host Shankar Vedantam uses the everyday example of a toilet to illustrate the "illusion of explanatory depth," a cognitive bias identified by psychologist Phil Fornbach. He points out that while most people feel confident they understand how a toilet flushes, they cannot actually explain the mechanics, such as how the bowl empties without a pump or why it doesn’t overflow when filled. Vedantam expands the insight to broader domains—political policies, economic systems, and medical treatments—arguing that we often form strong opinions about complex topics without truly grasping their inner workings. He concludes by urging listeners to pause before drawing conclusions and to question whether they genuinely understand a subject, and invites them to explore more mind‑science content on Hidden Brain.

Chapters

Do you know how a toilet works? Surely, right? You push the handle, water flows, everything disappears. Simple. But how does the bowl empty without a pump? If you pour a lot of water into the bowl, shouldn't it overflow and make a mess on your floor? Maybe you don't actually know how a toilet works. Cognitive scientist Phil Fornbach calls this the illusion of explanatory depth. We mistake familiarity for understanding. Because we use a toilet every day, We assume we know how it works. But using something and understanding something are completely different things. This doesn't just apply to toilets. It applies to political policies, economic systems, medical treatments. We form strong opinions about things we can barely explain. So perhaps the next time you start to draw conclusions about how something works, ask yourself, do I actually understand this? Or do I just think I do? For more insights about the science of the mind, tune into Hidden Brain on Apple, Spotify, or hiddenbrain.org.