The whole premise behind The Dark Knight is that Batman is scaring criminals into hiding. The Joker emerges, offering these cowardly criminals his services, because he’s the only one willing to go toe to toe with Batman. Both realize that one exists because of the other, and there is no Batman without a suitable villain. To borrow Moriarty’s quote in The Reichenbach Fall:
"Every fairytale needs a good old-fashioned villain."
The Reichenbach Fall has the same premise. The first few minutes of the episode show how successful Sherlock is, solving crime after another and causing criminals to think twice before hatching any plans. As a result, the criminal underbelly is hesitant to make any moves. Moriarty emerges, showing himself as the only one who can go toe to toe with the Reichenbach hero himself. In a series of elaborately designed schemes, he successfully discredits Sherlock, plastering his name all over the papers as a fraud. In one fell swoop, Moriarty has shown the world what he can do. Both Sherlock and Moriarty acknowledge that one exists because of the other. To borrow The Joker’s quote:
"Oh, you. You just couldn’t let me go, could you? This is what happens when an unstoppable force meets an immovable object. You truly are incorruptible, aren’t you? You won’t kill me out of some misplaced sense of self-righteousness. And I won’t kill you because you’re just too much fun. I think you and I are destined to do this forever."
We can all agree that even the dialogue is pretty similar. The Joker tells Batman that they need each other. Moriarty says the same thing to Sherlock. “You need me,” Moriarty states flatly, while The Joker gleefully tells Batman: “You complete me.”
At the end of The Dark Knight, Batman has fallen from grace, becoming a fugitive whose reputation has been sullied by the events surrounding Harvey Dent’s death. At the end of The Reichenbach Fall, Sherlock Holmes is no long a hero and genius detective, but a fraud, completely discredited.
Thought you guys might find this interesting.