So many jews and others allowed themselves to be passively led to the gas chambers and other deaths because the Nazi’s tricked them into believing there was a chance at survival. In night the reason why Elie never threw himself into the fence when he thought he was being led to his death is because he knew there was still the chance at him surviving, and he was right.
The key to survival at the death camps were to only care about yourself: if you spent your time focusing on keeping your family alive, your chances are diminished by great amounts. Elie had a much simpler time staying alive once his father died because he only needed to worry about his own health and his own strength; he no longer needed to worry about sharing his ration of food for the day and he only had to worry about himself.
When Elie writes that he became a “different person” in the camp, I believe he meant making the change from being a selfless person to a selfish person. At the beginning of the story Elie cared immensely about the survival of his family and felt extreme emotions when he watched his father going through painful experiences. Throughout the story Elie started to care more about himself and less about his father, as well as become desensitized to sights he once must have thought horrible. Having so many around you die every day no longer was seen as something horrible, just your average every day thing and being fed so little also became a custom he got used to. Elie began to adjust to the way the Nazi’s treated the jews and became accustomed to his living style at the death camps.