The Dunning-Kruger effect is a cognitive bias of overestimating one’s ability/expertise in a field when unaware of the unknown in the field.
AKA, the overconfidence effect – Confidence comes through the lack of knowledge (i.e. they don’t know what they failed to know or have the illusion of knowledge).
On the contrary, the effect also tells about the tendency of high performers to underestimate their skills/knowledge because they know what they don’t know.
Naturally, the less you know, the less you are aware of what you don’t know, then you’ll feel more confident about what you know.
The people who know more, the more aware of what they don’t know yet are the ones who have less confidence in their expertise.