Oddly Wired
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overconfidence

You systematically overestimate how much you know about topics.

The overconfidence effect is a bias where subjective confidence in judgments often exceeds objective accuracy, though this depends significantly on task difficulty.

It is not a 'consistent' bias; the effect is moderated by the hard-easy effect, as demonstrated in the cited research, where individuals are often underconfident in easy tasks.

Your certainty is often a measurement of your ignorance.

Where this comes from

Study
Lichtenstein, Fischhoff, and Phillips, 1982, Judgment Under Uncertainty
What the check found
The definition is standard, but the claim ignores the hard-easy effect, which is central to the very study cited.
Confidence
Solid, with limits
overconfidencejudgmentcognition

Related

One of these every day, and every one names the study it came from. When a finding is contested, it says so.