Shane Frederick's bat-and-ball puzzle is deceptively simple: a bat and ball cost $1.10 together, and the bat costs one dollar more than the ball — how much is the ball? Most people, including a majority of students at elite universities, blurt out 10 cents. It's wrong (the correct answer is 5 cents), and what makes the puzzle so revealing isn't that people get it wrong — it's that the wrong answer arrives with such immediate, confident fluency that most people never feel the need to check it.
Frederick built this into the Cognitive Reflection Test, which measures a specific tendency: how willing someone is to override a fast, appealing System 1 answer with the slower work of actually verifying it. The test's most striking finding connects this tendency to something seemingly unrelated — people who answer intuitively and incorrectly on these puzzles are also more likely to choose a smaller immediate reward over a larger delayed one, linking quick uncritical thinking to weaker impulse control generally.
Frederick administered his bat-and-ball puzzle and similar questions to students at some of the most selective universities in the world and found the large majority still gave the fast, wrong, 10-cent answer without checking their arithmetic. Kahneman connects this to a much earlier and now-famous study: Walter Mischel offered four-year-olds a choice between one small treat immediately or a larger treat later if they could wait alone in a room without eating the smaller one. Children's ability to wait predicted better self-control and life outcomes years later — and children who spontaneously used distraction strategies, like looking away from the treat, held out the longest.