Why does knowing it make you worse off? If you're a man, you're better off knowing it, because confidence can be increased by practice. If you're a woman, you're also better off, because you can better distinguish confidence from real skill in men.
If we consider the Dunning-Kruger effect, the majority of people who are confident of their abilities are more likely to be incompetent; thus perpetuating the confident buffoon mentality since they are more likely to find a mate compared to those who at least know that they are ignorant.