The Invisible Number

In a famous experiment, researchers had people spin a rigged wheel that stopped on either 10 or 65. Then they asked an unrelated question: "What percentage of African nations belong to the United Nations?" People who saw 10 guessed around 25%. People who saw 65 guessed around 45%.

A random number on a wheel, completely irrelevant to the question, shifted answers by roughly 20 percentage points. This is the anchoring effect, one of the most widespread biases in human thinking.

The first number you meet becomes an invisible reference point that pulls every later estimate toward it. Your brain does not judge a number on its own. It judges it against whatever number it saw first.