In Night by Elie Wiesel, discuss the importance of pessimism vs. optimism in the novel.

I think that the dynamic between optimism and pessimism is
a very important dynamic in the course of the narrative.  However, I do not see it as a
type of ultimatum or binary opposition.  Rather, the complexity of the work presents
both present at the start, with one being slowly eroded as the experiences build and
develop.  At the start of narrative in Sighet, Eliezer possesses a sense of optimism
with his studies and his belief in God.  As he experiences life at the different camps,
slowly, his optimism erodes and gives way to a more survivalist approach to
consciousness.  It is not that he becomes "pessimistic" about things, as much as he does
not fully understand the reason behind why those elements that defined his optimistic
nature are disappearing.  Life in Sighet, his community, his family, his faith in God
and God himself, are all elements that display Eliezer's loss in the elements that
sustained his belief.  At the same time, it might be interesting to note that Eliezer's
need to survive, driving his state of being, grows in strength as the work progresses. 
This might be seen as a form of positive thought or optimism, in that he seeks to
survive. Yet, Wiesel is keen enough to restrain from such easy distinctions.  Rather,
the drive for survival is shown as an almost animalistic end.  In this light, the theme
of pessimism and optimism is inverted entirely to an end where little is clear, much
like the Holocaust itself.