Game of Thrones this week holy shit!!!!!!!!!!!!!!!!! It was really, REALLY good. But right now I want to talk about a part of it that was maybe not so good.
Episode 7x03 - As the Unsullied are heading to Casterly Rock to take it over, we get a voiceover from Tyrion explaining that his father would only let him be in charge of the sewers of Casterly Rock, so he built them with secret passageways to sneak in lady friends. As Tyrion is telling us this very convenient information, we see the Unsullied making their way in through the secret passageways.
Now, granted, Tyrion did mention being in charge of the sewer system of Casterly Rock way back in season 2, so this VO wasn't entirely out of place. However, the convenience of it makes me, as an audience member, feel a bit cheated. Nobody's ever mentioned or canonically used the secret passageways at Casterly Rock until it became necessary, and I'm supposed to believe this was a plan from the start. I'm supposed to believe that the writers knew well in advance that the sewer system would be important, even though they're only mentioning it to me when it's needed.
This whole mess about Castery Rock's sewer system is immediately upstaged by the fact that nobody's even at Casterly Rock. Jaime Lannister taking over High Garden and murdering Lady Olenna made me completely forget about Casterly Rock, which is definitely what they intended. They could gloss over Casterly Rock, purposely make it easy for the Unsullied to get inside, only to surprise us with nobody being there. But just because the diversion was only a ruse to get us to go somewhere else (High Garden) doesn't mean it can't also be interesting. Just because this is the second time Game of Thrones has done the whole "the army's not where it was meant to be!!" trope doesn't mean they should've glossed right over it this time with a convenient plot device.
In the musical Book of Mormon, there's a song called "Turn It Off" where Mormon missionaries are singing about repressing their feelings and "sins." They break into a tap routine halfway through the song, and during the routine they clap twice and the lights go off. They clap again and the lights come back on and they keep dancing. Thirty seconds later, they clap again and the lights go off. When they clap to turn them back on, they're all wearing sparkly pink vests. Now, obviously the lights went off the second time because they needed to do a quick costume change without showing the audience. (I say "obviously" but actually my friend Michael pointed this out to me and I would've never noticed it myself.) But because they did the clap twice trick once without a costume change, I as an audience member (and a person who's worked in theater and should notice these things) wasn't sitting there thinking, "Oh they just cut to black so they could do a quick change, that's silly." They established that it was a thing before they needed it - so that I wouldn't be thinking about the fact that they needed it.
Conclusion: If you need something for convenience sake in your writing, you must establish it before you need it. If you bring it up only at the moment when it is required, your audience is sitting there thinking, "They just came up with this conveniently for this one part and for no other reason." And you never want your audience to feel smarter than you.