Sam Winchester always had a craving. His first memory was the smell of it, though he was kept in the motel bathroom with his brother, who prevented him from ever reaching the most wonderful smell in the world. He was two years old.
It wasn't until he was nine years old when he finally found out what that wonderful smell was. He wondered how good it tasted, how great it could make him feel. His father and brother had just killed something on their last hunt, though Sam had waited in the car.
When Sam was thirteen years old, he finally had his first taste. He had been tracking the demon for weeks, when his family happened to end up in the same state as the thing. It took a lot of courage to run away from his brother to track the demon, but it was well worth it.
The blood made him stronger than ever, both physically and mentally. He did better when he trained with his brother, and had even started having flashes of what was going to happen, saving his family multiple times.
As soon as Sam turned sixteen, he dropped out of school. His father and brother were constantly on hunts, and Sam was tired of school getting of the way of hunting. It was much easier to sneak out to hunt now that he could drive, which was more often now, as he needed more blood, with fewer days in between.
Two years later, Sam parted ways with the family he was with for so long. He hunted by himself, nothing but the stolen car and weapons to his name. He didn't talk to his family for four years, when his brother and him and met up on a hunt. Dean filled Sam in on the past years, including their missing father.
A year after their father's death Sam and Dean met Ruby. While Dean was weary, and distrustful, Sam was using all his willpower to not lunge at her and her sweet-smelling blood that could do so much for him.
When Ruby had suggested he use his powers that had naturally lies within him, Sam had quickly agreed, although he had made sure his brother was not anywhere to be heard. With Ruby on his side, his power grew, and he was able to kill demon with hardly any effort at all.
Sam Winchester was the most powerful human alive, stronger than any witch or warlock, could defeat any demon with the blink of an eye.
All while his addiction to demon blood grew.