Being a football player is not the diametrical opposite of being a football coach. Likewise, being a researcher doesn’t exclude the teaching role; more often, it entails a teaching role.
But it’s interesting to recognize also that being a player is quite different from being a coach. And what makes a good researcher is not necessarily what makes a good teacher.
The #1 goal of a decent player (with a reasonably competitive mind) is to be the #1 player. But it’d be strange to say that the primary goal of a coach is to be the top coach.
Researchers seem to be motivated by his or her own curiosity and obsession with knowledge. But these are not necessarily, if not rarely, what motivates most teachers.
On the other hand, what teachers care about most is how to motivate students and how to transmit his knowledge in the most effective way possible. A researcher may not be motivated by these goals at all. In fact, some couldn’t care less about them.
As they have different goals, I figure it’s reasonable they not be judged using the same yardstick.
(Image from http://uk.reuters.com/)
If it’s ok for Beckham not to be a good coach (or not becoming a coach at all), it should be ok if Ferguson doesn’t know how to play football.