Cognitive biases: why a smart brain makes the same mistakes every time
Mental shortcuts: why your brain guesses before it thinks
A bat and a ball cost $1.10, and the bat costs $1 more than the ball. More than half of the students at Harvard, MIT and Princeton got the price of the ball wrong. Meet the shortcuts your brain takes before it thinks.
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Miva wants her first car, and a new one costs too much. So you come along with her to a used car lot. Rono sells the cars there, and Miva knows nothing about engines.
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She does not open a single hood. A rusty door: no. A flat tyre: no. A clean yellow car: that one! Her brain has picked before she starts to think.
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That quick guess is a mental shortcut: a few clues stand in for the long check. Scientists call it a heuristic, and every brain uses them all day.
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And most days, the shortcut is right: a car with rust outside was often badly cared for inside too. Each guess that works makes the next one feel safer, so she checks less and less.
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Beside the yellow car, Rono has put up a sign for his car wash. The numbers look easy, and Miva's answer jumps up at once: the wax costs $10. It feels just as sure as the rusty door did.
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You check it slowly. With $10 wax, the wash costs $110 and the total is $120. The wax costs $5. The same puzzle, with a bat and a ball, tricks more than half of the students at Harvard, MIT and Princeton.
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When a shortcut is wrong, it tends to be wrong in the same way, and it feels just as sure as when it is right. So even a smart brain makes the same mistake again and again. And Rono has sold cars for twenty years.
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Go further
A few names behind the story.