Strength

Sam and Dean Winchester had one weakness. Each other.

They knew it, their friends knew it, even other hunters knew it. Unfortunately, an alarming number of their enemies knew it, too.

Point a gun at Sam, and Dean would jump in front of the bullet.

Try to run Dean over with a truck, and Sam would push him out of the way.

Kidnap Sam to use as bait, and Dean would walk straight into the trap.

Hold a knife to Dean's throat, and Sam would back off immediately.

Torture Sam for information, and Dean would spill every last detail.

Capture Dean, and Sam would surrender.

Abduct Sam, and Dean would be frantic with worry until he was found.

Injure Dean in a fight, and Sam would drop everything to check he was okay.

Threaten Sam's life, and Dean would kill for him.

Tell Sam that Dean was dying, and he would do anything to save him.

Kill Sam, and Dean would sell his soul to bring him back.

Condemn Dean to hell, and Sam would be so consumed with grief that he would allow himself to be led down a dark path of self-destruction.

Divide the brothers with lies and distrust, and they would inadvertently bring on the apocalypse.

They knew the severity of the situation. They realised that the dangerously co-dependent nature of their relationship had put the entire planet in jeopardy, and they were all too aware that if they did not find a way to overcome their weakness it could mean the end of the world.

But you couldn't spend a lifetime protecting someone, sharing everything with them, living and laughing and hurting and crying with them, knowing you had nothing but each other, loving the other person more than life itself… and then just let them go.

Not easily. Not without being ripped in half and knowing you could never be made whole. Not without feeling a pain worse than all the tortures of hell. Not without dying inside.

The fate of the world hung in the balance.

So, even though every fibre of his being screamed at him to save Sam at all costs, Dean knew that this time the cost was too high. This time he couldn't be selfish. He couldn't be weak.

He had to let Sam say yes to Lucifer. He had to let Sam go up against the devil – alone – in a battle for humanity's very survival. He had to accept that Sam would either destroy the word or fling himself willingly into eternal damnation. He had to accept that, no matter how this ended, he was going to lose Sammy forever.

It was unbearable, unthinkable, but Dean had to.

So he did.

Their enemies laughed at them. They believed victory was theirs. They believed the Winchesters had finally been defeated.

But they only knew of their weakness. They did not realise that there was far more to the brothers' relationship than even they themselves knew.

It wasn't until Sam wrested back control of his body that the truth was revealed.

In that last moment before Sam fell backwards into the abyss, the gazes of the two brothers locked. They needed no words. Sam's eyes said everything.

Dean, you were my strength.

And then he was gone.

It was all over. No one would ever know how close they had come to Armageddon, or what the brothers had sacrificed to save the world.

Dean had lost everything.

Battered, bruised, broken and bleeding from wounds both visible and unseen, Dean knelt in the patch of dead grass, head bowed, shoulders shaking. A lone tear slipped down his cheek and fell to the earth.

All this time, he had thought that Sam was his greatest weakness.

He was wrong.

They had been stronger together.