"No," he shakes his head, curling in closer and just trying to breathe through the discomfort. "Not strong enough. If I was I wouldn't be here. Wouldn't be.. sick. 's the demon blood Dean. Ever since I was a kid. Can't shake it, can't shake it. I'm not right."

Because it was the blood in the end. Azazel's blood that tainted him when he was just a child. That's why Dean was stronger. Why he'd always be stronger.