The Number That Sticks

Kahneman and Tversky spun a rigged wheel that landed on either 10 or 65, then asked people to estimate the percentage of African countries in the United Nations. People who saw 10 guessed around 25%. People who saw 65 guessed around 45%.

This is anchoring bias: the first piece of information you receive disproportionately influences all subsequent judgments. Your brain treats the initial number as a starting point and adjusts from there — but the adjustment is almost always insufficient.