When Elrond was younger, he almost drowned trying to get to his parents who resided in the sky.
It wasn’t to return to them or anything like that, he had already found his own ways to deal with the fact that they weren’t coming back for him. Rather, it was to retrieve the Silmaril in order to help Maglor and Maedhros fulfil the Oath.
Though the brothers tried to hide the toll of their Oath the best they could, early on, Elrond and Elros could already tell that the stress of it was getting to them, deteriorating their health and driving them insane.
So one day, Elrond pulls Elros aside and concocts a plan.
mother could turn into a seagull, than perhaps I can too, and I’ll fly to the
sky and retrieve the Silmaril, then bring it back! I’m not sure how long it
will take, but you’ll know when I return. When I do, I’ll give it to them, and
everything will be okay!”
Logically, it makes sense to both twins.
So early in the morning, Elrond and Elros leave the fortress and walk to a cliff. It’s not too tall, but not small at all, certainly huge for a small elfling. The tides below are worse in the morning, and beating themselves against the rock.
“If you’re scared Elrond, Its okay. They won’t be mad at us if you don’t go.”
Though Elrond shakes his head and removes his shoes, “I’m not scared, I can do it,” he says happily, and repeats, “And when I get back, things will be better!”
So Elrond jumps. And Elros waits for him to turn into a bird, waits for Ulmo to save him, and waits to see a white gull energy into the sky. It doesn’t happen.
He waits for a bit longer, getting nervous and scared. And when nothing happens, he runs back to the fortress, runs as fast as he can, slamming into Maedhros who’s walking down the hallway. He’s mixing common tongue, quenya and sindarian up together in the midst of sobs, grabbing at Maedhros’s stump and dragging him to the shore.
By the time they get there, Maedhros’s men have already dragged an unconscious Elrond out of the sea.
After bringing him to a healing chamber and ensuring his safety, he makes Elros tell him what the hell happened. When he finds out why he did what he did, Maedhros can’t be as angry as he wants to be at him, not at all. He’s just devastated.
Maglor runs into the healing wing, hair a mess and robe loosely tied around him. He demands to know the story as well, and of course, he’s not as calm and collected as his brother. His fear of what could have happened to Elrond fuels his anger, and he actually terrifies Elros.
After calming him down, Maedhros explains what happens, and Maglor almost feels like crying (later on he asks Maedhros whether or not their presence has cursed Elrond and Elros, for certainly it makes no sense that Ulmo would not spare them). Then, after speaking to Elros, Maedhros and Maglor try their best to explain why their idea didn’t work and how the Oath is theirs, not Elrond or Elros’s, and they should never, ever feel obligated to fulfill it.
Later Elrond wakes, sick and nauseous from the cold and a head injury. Though he’s conscience enough to hand the Feanorians a shiny rock he found before he hit the stones.
“It’s not a Silmaril but I hope you like it.”
Maglor has to leave the room, and Maedhros actually gets choked up.
Of course Elrond gets the same rundown as Elros did later on.
(later on they break the rock in two, and both Maglor and Maedhros wear it as a necklace)