One of Elie's greatest internal conflicts arises from his feelings towards his father. Elie loves his father very much, but due to his nightmarish experiences of life in Auschwitz, he comes to see him as somewhat of a burden. The normal relationship between father and son has been completely reversed. Now it is Elie who must exercise parental responsibility over his sick and aging father.
The problem, however, is that Elie is unable to do this, as he himself is no less subject to brutal treatment at the hands of the Nazis. That being the case, he's forced to look out for himself and do whatever it takes to survive in such a harsh, pitiless environment.
When an SS guard beats Elie's father within an inch of his life, Elie's natural instincts are to help him. But at that point he's so apathetic, so tired, and so constantly tormented by extreme hunger that all he can do is look on helplessly. Even when his father passes away, Elie doesn't shed a tear. All he can think about at such a sad moment is where his next meal is coming from.
It's clear from the way he writes about these experiences that Elie has never fully been able to reconcile this particular internal conflict, and that guilt prevents him from doing so.