The Roulette Wheel Experiment

Daniel Kahneman and Amos Tversky rigged a roulette wheel to land on either 10 or 65, then asked people to guess the percentage of African countries in the United Nations. People who saw 10 guessed around 25%. People who saw 65 guessed around 45%.

A completely random number — from a roulette wheel — shifted people's estimates by 20 percentage points. The subjects knew the wheel was irrelevant. It didn't matter. Once your brain registers a number, it quietly adjusts from that starting point.