I came to this view of because people insist on viewing my various behaviors through the framework of confidence. When I have a realistic view of my ability to do some particular task well, I am labeled confident, as opposed to simply accurate. When I predict that I would be below average at some particular task, based on years of knowing myself, I am labeled unconfident when in fact I am simply right or wrong. Where does confidence come in?
I would extend this to optimism/pessimism - I hate those terms. They're both... useless.