Knowing how sure to be
Being right is one skill. Knowing WHEN you are right is a second, separate skill, and almost nobody has ever had it measured.
After every answer, a feeling arrives with it: sure, or not so sure. That feeling is itself a kind of answer.
The feeling can be checked: collect the sure answers and count how many were really right.
People who see their own count start matching sureness to truth. The feeling is trainable, like a swing is.
Then and now
What began as a survey curiosity is now a measured ability with its own scoring rules, studied separately from the skills it sits on top of.
Lichtenstein, S. and Fischhoff, B. (1977)
Where it began“Do those who know more also know more about how much they know?”
Organizational Behavior and Human Performance, 20, 159-183
People's sureness routinely outruns their accuracy: on hard questions, answers given with total certainty were wrong far more often than the certainty allowed.
Fleming, S. M. and Lau, H. C. (2014)
State of the art“How to measure metacognition”
Frontiers in Human Neuroscience, 8, 443
The modern measurement standard: knowing-that-you-know can be scored separately from task skill, and the two really are different abilities.
What we do and do not claim
Knowing how sure to be is a skill about your own answers. It says nothing about how smart anyone is.