Base Rate neglect
Etymology
A base rate is the underlying frequency of something in a population; neglect is Latin neglegere, "to disregard." The bias was pinned down by Daniel Kahneman and Amos Tversky in the 1970s, whose famous problems (the shy "librarian or farmer," the taxicab case) showed people leaning on a matching stereotype while ignoring the raw odds.
noun phrase · /BAYS RAYT nih-GLEKT/
Ignoring how common something is in general when judging how likely it is in a specific case.
What it names
Why a vivid detail can overwhelm the statistics — we forget to ask "but how often does that actually happen?"
Example
A positive result on a rare-disease test still usually means you are healthy — base rate neglect is why that feels impossible.
Related idea
Representativeness heuristic is the engine: we judge by how well a case fits a type, which is exactly what pushes the base rate out of view.