> I can’t remember of DK suggests some sort of effect where the expert has undue self-doubt, though…

There is a brief bit where they attribute that observation to other causes:

In making these predictions, we felt that we could account for an anomaly that appeared in all three previous studies: Despite the fact that top-quartile participants were far more calibrated than were their less skilled counterparts, they tended to underestimate their performance relative to their peers. We felt that this miscalibration had a different source then the miscalibration evidenced by bottom-quartile participants. That is, top-quartile participants did not underestimate themselves because they were wrong about their own performances, but rather because they were wrong about the performances of their peers. In essence, we believe they fell prey to the false-consensus effect (Ross, Greene, & House, 1977). In the absence of data to the contrary, they mistakenly assumed that their peers would tend provide the same (correct) answers as they themselves—an impression that could be immediately corrected by showing them the performances of their peers. By examining the extent to which competent individuals revised their ability estimates after grading the tests of their less competent peers, we could put this false-consensus interpretation to a test.

Link if you need it:

https://www.researchgate.net/publication/12688660_Unskilled_...