In "Unskilled and Unaware of It: How Difficulties in Recognizing One's Own Incompetence Lead to Inflated Self-Assessments," David Dunning and Justin Kruger state that the less skilled or competent you are, the more confident you are that you're actually very good at what you do. Their central finding is not only do such people reach the erroneous conclusion and make unfortunate choices, but their incompetence robs them of the ability to realize it.
This, of course, is true of everyone in some way. We think we have a great sense of humor when we don't. We rate ourselves higher than others in a variety of skills
Lake Wobegon - where all the children are above average
Turns out though that less competent people overestimate themselves more than others.
The reason is the absence of a quality called metacognition, the ability to step back and see our own cognitive process in perspective. Good singers know when they've hit a sour note, good directors know when a scene in a play isn't working, and intelligently self-aware people know when they're out of their depth.
When I hear unsubstantiated claims, usually from sole proprietors, working on de minimis projects, I think of Dunning-Kruger. I've vowed to ignore them and move on. If it works in their domain, then any advice they provide is usually limited to their domain and their experiences in that domain. But the continued chant that certain processes, methods, fixing for dysfunction continue. Getting louder when they are asked to show the evidence their idea has a basis in principle. This is the confirmation bais for their misunderstanding of the principles on which they are making their claims.