Generally, it is people with a lower ability to understand the world that overestimate their own intelligence because they are unable to imagine anyone being smarter than them, and those on the smarter end who underestimate their own intelligence because they believe everyone else must be able to see what they are able to see.
There was a paper, quite famous now, on the topic titled "Unskilled and Unaware of It: How Difficulties in Recognizing One's Own Incompetence Lead to Inflated Self-Assessments"
I feel like hearing this is dangerous in itself - even if you overestimate yourself, surely you yourself don't overestimate yourself as much as others?
Personally, I ran against a closed glass door yesterday. All I hope for is that I was entertaining to onlookers at least.
It's when you don't have the capacity to know how dumb you are that you overestimate yourself, and you overestimate yourself (and underestimate others) far more than those able to see how dumb you actually are. It's when you are smart that you overestimate others, and underestimate yourself.
There are limits to this, plainly Einstein didn't think some guy as dumb as a bag of rocks was as smart as he was.
Funny story about that - there's a hotel in Edinburgh originally built in the mid-1800s, which was gutted and renovated with a lot of facade retention and architectural salvage to keep the look of the place. The centrepiece was the ornate brass and mahogany revolving door.
But when it was finished people kept walking into it the wrong way and getting stuck, and no-one could figure out why.
Eventually they sussed it out - until the early 1900s, no-one standardised on which way revolving doors go. Now, of course, they turn anti-clockwise - you pass people going the opposite way on your left, don't you?
There was a paper, quite famous now, on the topic titled "Unskilled and Unaware of It: How Difficulties in Recognizing One's Own Incompetence Lead to Inflated Self-Assessments"