If you are a poor performer, chances are that you wouldnt be aware of it

Seems intuitive and sensible. Now there is ample proof for it too.

"
In a logic test administered to people who had volunteered over the internet, a team of researchers found that the lowest scorers vastly overestimated their performance, believing, on average, that they had gotten 7 out of 10 items right, when the actual figure was 0, according to Thomas Schlösser of the University of Cologne in Germany.
"

I find that most interesting. Through HBR