Do you understand bicycles?
During one study participants were asked to draw a diagram of a bike. The results were disastrous. Many drawings were physically impossible. After struggling with the drawings participants realized they did not understand bikes as well as they thought.
Yale psychologist Frank Keil has nicknamed this phenomenon the illusion of explanatory depth. It refers to our tendency to overestimate how well we understand something and to correct this mis-appraisal after we try (and fail) to explain how it works.
In another study, participants were asked for opinions on political issues like single-payer healthcare or a cap-and-trade system for limiting emissions. They also rated their understanding of each issue. Then, all were asked to explain the issues in depth. Afterward, people consistently downgraded their estimates of their own understanding and became more moderate in their views.
Others in the same study who were asked to defend their position instead of explaining the issue did not demonstrate this effect.
So, next time someone is spouting off her opinion about something, a better approach than directly challenging her might be to ask, “how does that work exactly?” She will likely adopt a more moderate stance as she tries to explain it.