Why do so many NEETs believe they’re not smart?

I lurk here often as a non NEET because in my life, I’ve resonated with a lot of the common feelings mentioned in this sub about hopelessness, lack of purpose, etc. (If this doesn’t apply to you in particular, that’s awesome.) But one thing I found interesting in particular is that so many NEETs say that they’re not intelligent, sometimes debilitatingly so. I live in one of the least educated parts of the US, and here a majority of people couldn’t pass an 8th grade math or spelling exam. These are business owners, managers, teachers even. I read posts from NEETs mentioning their lack of intelligence and it seems so surprising because just from reading the posts, most of you are better spoken and more insightful than most people I encounter on a daily basis. This makes me wonder, does this perceived lack of intelligence come from an overall lack of self esteem, or are you genuinely considered by others to not be very smart? If it’s the latter, coming to Louisiana may fix this lol.