Context comes out of nowhere, and leaves more questions than it answers
Not so much a character trope as a storytelling one that affects character development. Spoilers, obvs.
- Spirit Bending/The Lion Turtle | Aang | Avatar: The Last Airbender
Aang, a non-violent monk needs to defeat Ozai without violence. A lion turtle, creatures that were never set up or explained even once in the show, shows up at the last minute to give Aang the ability to spirit bend and strip Ozai of his fire bending. The context is solidified in Legend of Korra, when we learn all bending was a gift from lion turtles, but remember, LoK came out years after ATLA. So it was really a huh? Wtf just happened moment when it first aired. Moreso, how did no one know about the lion turtles? The whole point of the Avatar is they are actively connected to the past. They didn't pass this information down? Knowing at some point harmonic convergence would happen again?
- The Elder Wand/Wand Lore | Harry Potter | Harry Potter and the Deathly Hallows
The Elder Wand changes allegiance to whomever conquers its weilder. So Dumbledore dominated Grindelwald, then Snape dominated Dumbledore, so Voldemort killed Snape, but actually the wand answered to Harry because Draco disarmed Dumbledore (who was not, even once at Draco's mercy since he knew what was happening and let it), and then Harry disarmed Draco using a completely different wand so actually he was its master the whole time? Not to mention wand lore is never addressed (which you'd think would be taught to first years because the world relies on wands), and *people disarm each other all the goddamn time in this series* but never forfeit control of their wands in doing so. It's irksome because Harry inherits the cloak, which makes sense. He literally dies to master the stone. Which makes sense. But then to become the master of death and defeat voldemort he only had to disarm... Draco? Huh?
- P.L.E.A.S.E | Barney Stinson | How I Met Your Mother
He was a peace loving hippie in love. We see his past where he got his heart broken because his girlfriend ran off with a suit so he became a suit and also a womanizing gigalo. And after how many seasons was it? 8? Of being shown how disgusting and selfish a person Barney is, it's revealed that actually he was working for the FBI to take down his boss who also happens to be the man his girlfriend ran off with. So which was it? Was he so broken he became the enemy because the enemy had power? Or was he just a good guy helping his country (with the added cherry of petty vengeance). This one is a bit milder, because it does actually answer some questions. Like how Barney got away with his numerous crimes without the slightest consequence, or how he orchestrated the airport bullshit. Why he couldn't talk about his job, and how he got such an elite position when he was seemingly an uneducated wanderer before. But it still does not make a shred of sense for his character, and seems like it was forced in there to retcon how much of a piece of shit he is.