If we only know little, we think we know a lot. If we know a lot, we think we only know little. When we are incompetent at something — either a task or a field of knowledge — we, by definition, lack the skills to assess our own ability properly. If we’re not smart enough to fully grasp the magnitude of the issue at hand, we tend to also not be smart enough to fully grasp our ignorance. This can quickly lead us to overestimate our own competence. We need some expertise to recognize that we lack it.
One of the best ways to learn one's ignorance is to have a set back. When things that were so easy become difficult, it takes courage to learn again. And when things that were difficult become easy, it just blows your mind.
Always a good reminder.
Typical mentions of DK revolve around incompetence. Much more interesting in my opinion is the effect on competent/smart individuals - nice to see that here!