Spoiler and Over Analysis of a Fictional T.V. Show. I'm currently watching Season 5 of Supernatural. In the first season of the show, the character of Sam seems kindhearted, vulnerable, and compassionate. The actor, Jared Padalecki, has both an expressive face and eyes that convey care and other emotions without dialogue. Dean, Sam's brother and co-fighter-against-evil on the show, jokes about the power of Sam's "puppy dog" eyes to melt intractable hearts on several occasions. Sam seems to show genuine concern for the victims of the demons and supernatural villains that he and his brother hunt.
Throughout the first season, Meredith, Pat (I think) and I claimed Sam as our favorite character. Meredith and Dave jetted through seasons of the show. After watching Season 5, Meredith told me that Sam seems caring on the surface, but he's actually overcompensating for the evil within him. When I initially heard Meredith's opinion, I felt like she was reading a great deal into the demon blood angle. (Long explanation. If you watch the show, you understand. If you don't watch the show, the demon blood plot thread is too much of a tangent for me to explore right now.) Then, I saw the episode in the fifth season in which Dean goes forward in time.
The Apocalypse is underway. Dean arrives in a future in which human survivalists group precariously together in makeshift encampments, in ever decreasing numbers; demons triumph; a virus has turned huge numbers of people into zombie-like creatures; and future Dean is a hardened, callous jerk. Satan needs to possess a body to walk the Earth and specifically has sought Sam's body as the most suitable vessel. Bound to respect free will, Satan can only take over Sam's body with Sam's assent. In this future world, Sam and Dean were estranged for a number of years. Sam felt alone and full of self-loathing. In a moment of weakness, he permitted Satan to possess him. After Dean experiences this future, he returns to the present and decides that he must reconcile with Sam. Dean believes he can change the future because of his faith in his bond with Sam and in human goodness. He also looks at the angels as self-interested and arbitrary. Dean refuses to be the pawn of the angels and to allow the Archangel Michael to possess him in the name of countering Satan. OK - convoluted synopsis, but it gets me to my point.
In that future-jumping episode, you see Satan in Sam's body for 10 minutes or so. Satan speaks in serene tones, smiles sweetly, and gives gentle looks. It's creepy. And the front of kindness is presented by Satan from Sam's body. The mannerisms of Satan were Sam's mannerisms. After watching that episode, my view of Sam shifted subconsciously. I didn't expect the shift, but, as I watched the next couple of episodes, I felt less comfortable with Sam. I now see Sam's concern and kindness as being more of a superficial facade, as the camouflage hiding the anger and evil that Sam is fighting to contain. I now look at Sam as a wild card. In one episode, after 4 full seasons, Supernatural altered Sam from an innocent, kid brother to a volatile, pained man.