[Jensson]

Intermediate knowledge of what's being tested, everyone is the most overconfident on subjects they have intermediate knowledge about.

If you test high school concepts then if you are shaky about high school concepts that applies to you. People who have no clue about high school and people who understand high school well will be less overconfident on that test.

Or if you talk about college algorithms, then that is the basis for intermediate knowledge. An average comp sci grad will be the most overconfident, a person who never studied algorithms and a person who teaches algorithms for years will be less overconfident on that test.