The Dunning–Kruger effect is a cognitive bias manifesting in two principal ways:The Wikipedia page is blessedly terse and clear, and well worth a read. Also, it shows that I'm far from the only person to have independently noticed this via observation and intuition (see the "Historical References" section). But I believe Dunning and Kruger have pinned down only a chunk of a larger problem - one this Slog often blunders around and obliquely alludes to, without ever quite nailing it.
Unskilled individuals suffer from illusory superiority, mistakenly rating their ability much higher than is accurate. This bias is attributed to a metacognitive inability of the unskilled to recognize their ineptitude.
Those persons to whom a skill or set of skills come easily may find themselves with weak self-confidence, as they may falsely assume that others have an equivalent understanding.
The related Impostor Syndrome is, in my view, a feature rather than a bug. One's failure to "internalize ones accomplishments" is another way of describing a reluctance to puff up into an arrogant putz just because something's gone well for you. Arrogance is elective, and I feel tremendous dismay for a society that would deem someone damaged for choosing another route.
There's no surer way to dry one's flow, to kill the golden-egg-laying goose, than to take one's temperature; to live in one's own contrails; to sniff one's own farts. Or to forget Banksy's wise observation that doing inspired work to garner acclaim is like eating a great dinner in order to take a shit.
Pardon my vulgarity, but I find the assumptions behind Impostor Syndrome too repulsive for more genteel terms.
Here's a list of more-or-less related postings.