Why does a good description make you forget the odds?
A vivid story feels like proof, so the actual numbers quietly disappear.
Base-rate neglect is ignoring how common something is in the first place when a specific, fitting description is in front of you. The background frequency - the base rate - is the strongest clue you have, but a portrait that matches a stereotype overrides it and pulls your guess toward the stereotype.
Your friend is quiet, loves books, and tidies his shelf by topic. You guess librarian - but there are far more clerks and salesmen than librarians, so by sheer numbers he is probably one of them.
Before a vivid description sways you, ask how common each option is to begin with.
A rare disease, a fraud alert, a perfect-sounding candidate - the description grabs you, but the base rate decides the odds. Anchor on the frequency first.
Story loud, base rate quiet - turn the numbers back up.
Learn the idea and practice English at the same time.