The first number you see quietly drags every later guess toward it

Anchoring is the tendency to rely too heavily on the first piece of information offered when making estimates, even when that number is arbitrary. In a classic 1974 study, Amos Tversky and Daniel Kahneman spun a rigged wheel that landed on either 10 or 65, then asked people to estimate the percentage of African countries in the UN; those who saw 65 guessed far higher. The wheel had nothing to do with the question, but it anchored the answer anyway.

— Amos Tversky and Daniel Kahneman, Judgment under Uncertainty: Heuristics and Biases — Science, 1974