On that night, that night that changed everything, four year old Dean began to build a wall.
He heard his mommy scream and his daddy yell and the roar of the fire. He felt Sammy in his arms and heat on his skin and grass under his feet. He smelt his house and his toys and his mommy burning.
So in the firelight, holding his brother and looking up at the flames, he began to build a wall.
Night after night, snuggled uncomfortably next to Sammy's crib, he built a wall around both of them. To protect them. To keep them safe. And only when it was completed did he start to talk again.
Eventually Dean realised there was only space for one behind his wall; Sammy began to try and brake free. To hug his dad and be loved by him and ask why? Why? Why? Why? And every time John said, 'Dean, don't cry in front of your brother, Dean, don't let your brother see you weak, Dean, don't let your brother know what we fight.' A brick was placed between him and Sammy.
The years went by and the wall turned into more of a circle encompassing Dean and the ever growing pile of crap strapped to his back. Every time John lost his temper, or stumbled in drunk, or couldn't bear to look at Dean, the wall was only strengthened. When Sam left him for Stanford the very foundations were rocked, but he rebuilt it. Stronger than ever.
There are downsides to being stuck on your own with only your crap for company. No one can ever hurt you because you don't let them get close to you. No one can ever let you down because you can't trust them in the first place. But you keep building, keep making it stronger, because it doesn't work. Those few individuals, your family. They still find ways to hurt you. To break you, even if they don't mean to.
So you keep building, in the hope that one day, you will stop hurting. Stop feeling anything at all.