Other than a complete lack of skill, I have found the most likely reason I couldn't be a professional baseball player. It would be my natural inclination to call Brian Bannister, for instance, "Brian" if he was my teammate.
Listen to a few interviews with his team or manager, however, and you will learn that he must forever and always only be called "Banny". The nickname phenomenon in the baseball clubhouse is astounding and lacks a staggering amount of creativity. I don't think I could be a party to it.