"I never get your limits, Watson. There are unexplored possibilities about you."We are in deep waters here, for this quote is doubly ironic.
-- Sherlock Holmes, "The Adventure of the Sussex Vampire"
On the first level there is the intended irony -- or perhaps even sarcasm -- on the part of Holmes. The detective would seem, out of context, to be paying a high compliment to his old comrade in arms. But he's actually putting him down. He's saying that Watson is incredibly naive for believing that "Big Bob Ferguson, the finest three-quarter Richmond ever had" was really seeking help for a friend, not for himself.
And I suppose he's right.
But there's also a double irony here in that what Holmes says is truer than he realizes: Holmes doesn't get Watson's limits or explore his possibilities. He constantly throws the good doctor into situations in which he cannot help but fail -- and then blames him for failing! Yet he expects he him to be always available ("COME AT ONCE IF CONVENIENT . . . "), even referring to his later-in-life marriage as a selfish act!
On the subject of friends, Holmes told Watson in "The Adventure of the Five Orange Pips," "Except yourself, I have none." No wonder!