1- How and why

Dean never thought he was going to be anything special, he was going to follow in his dad's footsteps as a mechanic, get a wife, have 2.5 kids and then die without leaving so much as a footprint on the world around him.

However, when a car accident that kills his parents and hospitalises him and his younger brother leaves Dean with nothing more to do than sit in a hospital room watching Sams every breath, Dean finds out that maybe he's more special than he thought.