Just as planned!

So I've been browsing TV Tropes recently, and thoroughly enjoying myself. So, my question to you all is, what's your favorite tired old trope that gets used in whatever series?

Personally, I favor the Xanatos Roulette, as immortalized in the series Death Note.

Chekov's Gun is probably my favourite--where an element is introduced early in the story, and its importance (often huge importance) isn't revealed until much later.

TVTrope link