The Dunning Kruger Effect
This is a cognitive bias where those who are unskilled rate their ability much higher than it actually is. They lack the skill to rate their skill and unable to recognise ineptitude.
It's not understanding the depth or complexity of an area. You don't know what you don't know, to put it in Rumsfeldian speak.
This is one of those problems of perception that everyone thinks doesn't apply to them. They might be super knowledgeable about one area. But of course, experts in one field are not necessarily experts in every field.