Why do smart people make the same mistakes in the same way?

Smart people make the same mistakes in the same way because everyone's mind relies on the same mental shortcuts, and those shortcuts fail in predictable directions. That's what a cognitive bias is: not a random slip, but a systematic tilt in judgment. We judge how likely something is by how easily examples come to mind, or we latch onto the first number we hear. Usually that's fast and good enough. Sometimes it leads us astray, and always in the same direction.

The classic demonstration is "Linda". People read about a woman concerned with discrimination and social justice, then decide which is more likely: that she's a bank teller, or a bank teller and active in the feminist movement. Most pick the second. But that can't be more likely, because every feminist bank teller is also a bank teller. The description just feels more typical.

The idea came from two psychologists, Amos Tversky and Daniel Kahneman, in the early 1970s. They were so close that they flipped a coin to decide whose name went first on their first paper. Kahneman won the 2002 Nobel prize in economics for this work, and wrote that Tversky, who died in 1996, would have shared it.

Not everyone sees biases as flaws. The psychologist Gerd Gigerenzer argues many are smart rules of thumb that work well in real life. Either way, knowing your shortcuts helps you spot when to slow down.