I think you could call it a phenomenon - something that plenty of people experience but we're not exactly sure what's going on.
They've tried to test it empirically but I don't think the tests themselves are satisfactory because testing whether someone can guess a number or whatever - well even that gave a result of 51% - but it's not a good test because there's no real personal relevance so why should you be able to guess the right number.
What happened to me was I was working on a stained glass window for Rawat's Brisbane house. Near the end I was cutting the last strips of lead and was going fine but then I started to worry that I didn't have quite enough lead to finish. I decided to be very accurate in my cutting and got out the ruler, measured it and cut the lead 10mm too long and so I had to trim it. Damn. I don't just measure once I measure twice on the next piece. 10mm too long again! I dumped the ruler. I finished all accurate cuts from then on and I plugged the 10mm shortfall on the last piece with one of the trimmings and a nice big solder onto the join.
So that was when it started - my flirtation with the idea of crediting yourself with knowing what you know without knowing it. My eye was accurate without intervention - in fact when I resorted to checking with a ruler, I fluffed it. It's a confidence thing I guess.
It grew from there - the next thing you know I am thinking my instinctive reckoning is accurate and blimey yes, and what a shock that was. So very deeply yes, at least for me as the type of human that I am, my instinctive understanding of reality is better than what I can work out in my head, what I can see on the outside is not enough.