Polymaths often make lasting contributions to world knowledge. It is narrow-minded to say that you don't want to learn something because of some pre-determined notion that you might not be good at that thing. Of course, saying (or suggesting) that you are proficient in something when you know that you are not is not fair. I am a programmer, but I am also an amateur designer and an accomplished artist. I am also a wannabe mathematician and one day I will write about my own accomplishments if nobody else does ;)