"My name is Sayid Jarrah, and I am a torturer." There are no words more appropriate to describe Sayid; he is, unequivocally, as Benjamin Linus once said, "A killer -- capable of things most men aren't." Under his threatening surface though, there exists a man with feelings, a man that is not completely content with his ability. There are two completely different sides of Sayid: the beast, who is often unrelenting in his killing, and the gentle, remorseful, self-sympthetic man. All throughout the series, these two sides have battled within Sayid. They slowly corroded him and left him, as seen most recently in Recon, as a dark zombie that refused to come to a friends aid. Sayid's greatest, and perhaps only, threat is himself, and, right now, he is losing.
In that first Sayid episode, Sayid kills but for love -- the only catalyst against the murdering machine. In the beginning of the episode, Sayid appears to be wholly devoted to his job, and the torturing, seemingly, does not bother him tremendously. However, when Nadia makes her first appearance, Sayid realizes his inhumane actions, and eventually revolts against the older, rule-following Sayid by aiding in the escape of Nadia. Although, her escape is significant to Sayid's character, it is not the most important in this episode. With the first encounter of Nadia, we are granted a glimpse of the former Sayid -- most probably a child who was picked on severely in school. As Nadia notes, she pushed Sayid in the mud and picked on him (although it was because she had a crush on him. Sayid, like most, failed to notice that mud pushing was a sign of affection). And if Sayid was picked on by Nadia, (not trying to be sexiest here) chances are the guys of the school picked on him, most probably to a stronger extent, as well. Years of school have taught me what happens to those who are bullied -- eventually they release. Eventually, all the bullying Sayid endured released itself in the form of torturing. Had we been given a closer examination of Sayid's job as a torturer, I believe we would have seen a much angrier Sayid. But we aren't. Nadia stops that anger from releasing.
There is another hint of Sayid's past within that first scene with Nadia. Upon entering the torture room, Sayid pretends he does not recognize Nadia, and continues on with his torture regimen. It wasn't until Nadia admitted her crush that Sayid opened up to her. This may be a stretch, but the more I thought about it, the more certain I became. Unless Sayid was a recluse, which events on the island have proven the contrary, or he didn't recognize her, which, in my opinion, he did, then he would have immediately questioned her identity rather than proceed with procedure.
I believe Sayid's past at the school gave him the mentality to utilize his innate skill.
The Gentle Man
There is less concrete evidence to prove that Sayid has a gentle side; it is enough to suffice though.
Shortly after he was inducted into the Oceanic 6, Sayid married Nadia. In the little time we see Sayid with Nadia, he is happy -- an uncommon expression for the man. Unfortunately, that happiness would be ephemeral and the beast would be unleashed. The significance pertaining to Sayid's character stands in the juxtaposition of the before and after of Nadia's death. Happiness quickly turned to give-me-an-excuse-to-kill, which would be granted/used to an advantage by Ben Linus. Ben used Sayid to terminate anyone he wanted dead, and Sayid willingly did it for revenge. It is evident by his extravagant and unquestioning lust for revenge that Sayid once was happy with his life. Since Nadia, every time Sayid tortured or did something inhumane, he questioned himself. As with torturing Sawyer, Sayid later questions his decision and ultimately ends up chastising himself for it. Nadia instilled that within him. But since fate robbed him of his love and his life, he lets the beast run wild without question. Love stands as the only bulwark to the beast of Sayid.
It was the lack of love that created the beast, and it is love that can stand in its way.
The result: The Dark Zombie
Watching an emotionless face watch Claire struggle to strangle Kate was riveting. Sayid no longer cares for his life. He surrendered to the Man in Black, to evil as a last resort. Sayid is tired of fighting that battle, and only receives tranquility in the promise of Nadia, the promise of love. Man in Black promised him that and he acceded to kill Dogen. Love is the only thing that can revive the dead Sayid, and if the Man in Black fails to provide Nadia, Sayid is hopeless.
As Sayid put it, "I have no life. They took it from me." They took Nadia from him. They are the only ones who can give it back. They won't.