An Interjection

Watson: So why do you put up with him?
Lestrade: Because I'm desperate, that's why. Because Sherlock Holmes is a great man, and I think one day—if we're very very lucky—he might even be a good one.

[ photo courtesy of A Bit of Anything, http://book-of-flights.tumblr.com ]

Lestrade, one of the three friends identified by dear Jim Moriarty. 

And it's the classic paradox, isn't it? That Holmes becomes a good man by sacrificing even the appearance of being a merely 'great' man.