Puzzles
Four cards, one rule
Four cards lie on a table showing E, K, 4 and 7. Each has a letter on one side and a number on the other. Rule: if a card has a vowel on one side, it has an even number on the other. Which cards must you turn over to test the rule?
Reveal the answer
E and 7. Most people choose E and 4 — but the 4 can't break the rule (the rule says nothing about what's behind even numbers), while a vowel behind the 7 would. Fewer than 10% of people get this right: we instinctively look for confirmation instead of falsification.
— Peter Wason, Reasoning about a rule — Quarterly Journal of Experimental Psychology, 1968