How is that hard? Got 100% correct on my 100% guesses. 70% correct on my 60-70% guesses and about 50% on the 50% ones. Don't people do this naturally? It is so easy to know when you are sure, when you know it is probably right and when you have no idea at all.
I think I generally have a sense of how confident I am and yet I know I sometimes overshoot because I'm overlooking a detail or incorrectly remembering something.
A 99.9% confidence statement is still wrong 0.1% of the time. If you make one such a day then you ought to be wrong about it once per three years. I don't see that as a problem, of course I get surprised when it happens since it is rare but there isn't much more to it.
And there are even higher levels than 99.9%, many things you are basically never wrong about so we can't find the error bar.
Edit: I think it is good to compare your confidence in a thing to other things. Are you really as confident in this statement as you are in the layman interpretation of 1 + 1 = 2 (ie if you take 1 apple, add 1 apple now you have 2 apples)? Then you can say 100%. But most things are way below that level.
EDIT: oh I think I missed that this was specifically referring to the link. I read it as a general comment about calibrating confidence through one's life!
Is there more info about this site and what it’s intended audience and goals are?
Maybe it's just a bit English-speaking specific?