"In season one, when I heard about a myth or a legend, I would go research and see what I could find out, or ask the writers or ask some of the producers up here, but as it’s gone on, I’ve tried to remain true to Sam in that if Sam knows something about it, then I’ll try to find out, but if Sam knows nothing about it, then I try not to know either. Kind of like acting by default, you know? It plays on my face that I don’t know what’s going on because I don’t know what’s going on, so Sam in turn doesn’t know what’s going on. This has been a trial-and-error process over 140-some episodes and I’ve found it’s worked for me. What I do research is stuff specific to what’s going on with Sam, like for the episode where Sam doesn’t sleep, I looked up the effects of lack of sleep and what it does to your joints, what it does to your sense of reality. Or back when Sam was detoxing from demon blood, I looked up detoxing, detoxing from drugs, and alcohol, and found out what the tangible signs of it were and what the emotional and psychological effects of it were. So instead of focusing on what Sam encounters corporeally, I focus on what Sam encounters internally."
Jared Padalecki on playing Sam Winchester
Source: Supernatural Magazine, Issue #33, pg 14