Science Puzzle
The Wason Sequence
An experimenter has a secret rule for sequences of three numbers. The sequence 2, 4, 6 fits the rule. You can propose any sequence and the experimenter will tell you whether it fits or not.
Most people guess the rule is "even numbers" or "add two each time" and then test sequences like 8, 10, 12 or 20, 22, 24, which all fit. What would be a smarter testing strategy?
The Answer
The smart strategy is to test sequences that would break your hypothesis, not confirm it. The actual rule in the original experiment is simply "any ascending sequence", so 1, 2, 3 or 10, 20, 100 or 3, 7, 999 all fit, even though they are not even numbers.
Testing 8, 10, 12 only tells you that even ascending numbers fit. It never tells you whether odd numbers or big jumps also fit. A single test like 1, 2, 3 immediately reveals that the rule is broader than you thought.
This is confirmation bias. People naturally look for evidence that supports their current belief and avoid tests that could show they are wrong. Good scientific thinking does the opposite: it actively tries to disprove the hypothesis, because a hypothesis that survives a genuine attempt to break it is much more trustworthy than one that has only ever been confirmed.
The principle: Confirmation bias. The natural tendency is to seek evidence that supports a hypothesis rather than tests that could disprove it. Good reasoning deliberately tries to break its own ideas.