It's funny how Sam and Dean keep trading places. First it was when they were young. Dean would come in limping and beaten from their latest hunt which his younger brother wasn't old enough to go on, and Sam would patch him up. Except over the coming years, John had been training Sammy to fight demons and the other things-under-the-bed that no one wants to know about. This time it was Dean caring for Sam, bandaging his sprained and aching joints, feeding him soup when his fingers were crushed by the weight of things falling on them, and the feat that is fighting monsters. Many years later, Dean had made a demon deal to bring Sam back from the dead. He'd gone to Hell and come back, and his brother was picking up the scattered pieces of Dean's soul, trying to make him forget about the trauma of Hell. And then Sam was thrown into Lucifer's cage with Him and Michael. This shook up their world entirely, and Sam had only one way to cope with constantly seeing Lucifer. Hurting himself. Of course, this couldn't last forever, what with the cut from falling on the broken shards of glass healing, so he needed alternative methods. He'd taken to slicing open his skin just to earn a few hours sleep a night. He knew that he couldn't carry on like this, that his body would be littered in scars and he'd look disgusting. He knew. But nothing could calm him when Satan appeared in front of him. Whenever he could hear the man's taunts he would automatically reach for the pen knife he stored in his back pocket, and place it on his arm. Lucifer would throw insults at him as he cut, saying that he was pathetic, couldn't deal with it like a real man. Then his image would flicker, and he'd vanish. And in his mind, Sam knew that no matter the consequences, there was truly nothing anyone could do to persuade him that this was wrong. Because nothing was as wrong as having the Devil in your mind.

It was one evening in Wyoming that Dean noticed his brother was taking an unusually long time in the bathroom. He knew his brother liked to get a proper shower and dry his hair, but this was going beyond funny. Sighing, he threw down the T.V remote and dragged himself up off the couch. He wandered over to where Sam was, and knocked gently on the door.
"Sammy?" He called. No answer. He repeated himself, a little louder this time. A hoarse "Yeah, yeah, hang on." came from behind the locked door, and the next thing he knew was his brother grabbing hold of the door handle and nearly fainting as he stepped out. Dean grabbed his shoulders and hauled him over to his bed. "Sam? Hey. Sammy?" His voice was raised, panicked, as he waved hand in front of his younger brother's face.
"I'm fine, Dean. Honestly. Just stood up too fast, I think." Came Sam's reply. Dean nodded, worry still lacing his features. When he gently pushed Sam down onto the covers so that he was laying, Dean noticed blood on his brother's sleeve. He was about to make a snide remark about how unhygienic it was to not wash your clothes after a hunt when he noticed that the blood was fresh.
"Sammy? What happened to your arm?" He asked, gently sliding Sam's sleeve up. A weak arm tried to intercept him, but his brother purely did not have enough energy.
"Nothing, nothing." Sam hurried, trying to pull himself meagerly away from his brother's grip. A gasp escaped from Dean's mouth as he noticed more marks over his younger brother's arm, all in various stages of healing. Some were white, like they'd been there for years, and some were red, newer. Blinking back tears, the elder asked why. To which Sam just replied "It's the only way I can make him stop, Dean."
He disagreed with his brother, whispering that he'd protect him and make Lucifer stop, when both of them knew that there was nothing he could really do to ease the pain.

In the end, I think that's what lead to the Winchester's perish. They were so absorbed in comforting each other that they'd forgotten how to live themselves. Unlike every story you want to read, theirs has a much different ending. They were never in one place consistently enough to give Sam the help he needed, and he eventually passed. His brother had to burn the younger's corpse, and their car, and his laptop, and everything which ever kept sentimental value to either of the pair. Then, after two weeks of drinking, he finally burned himself. After all, there was nothing left for that boy. His uncle, his dad, Jo, Ellen, Castiel, Sam, his mom. Even Bobby, the man they thought to be invincible. They were all gone. He felt as though he'd served his time, he'd done his share for this world. It's a sad ending, really, what happened to two brothers so close. I suppose the most extraordinary lives always have the saddest, most unexpected endings, though. Don't they?