The Dunning-Kruger effect. This is a remarkable theoretical and proven phenomena.
I didn’t know they’d proven it:
is a cognitive bias in which people reach erroneous conclusions and make unfortunate choices but their incompetence robs them of the metacognitive ability to realize it.
Meanwhile, people with true knowledge tended to underestimate their competence.
Basically, people are so stupid they don’t even realise they’re stupid.
Read a lot more here, where I came across it.
I don’t think I need to say a lot more, it’s got sooo many implications and is really thought-provoking.