One of the central themes in Elie Wiesel's 'Night'- one of the hardest and most gut wrenching books one can ever read- is that of God's reasoning. Wiesel was sent to Auschwitz during the Holocaust, where his family perished. The unspeakable horrors he witnessed there made the pious and scholarly protagonist of the book, apparently a vicarious incarnation of Wiesel himself, question God's motives. This made him heart-rendingly question God's existence.
I believe that if I were ever in such a situation (and 'God forbid that I should never be'), I would rather not believe in God. The question of how those beings whom we call human beings could commit such unimaginable acts of depravity is itself a universally profound and most complicated questions to answer, and one that would easily wear out human reasoning of an entire lifetime. I would not want to make the question infinitely more disturbing and complicated by assuming the existence of God and asking how 'He' could allow such things. Understanding human beings is a paradigm that is enough for many lives, and I wouldn't want my helplessness to grow many orders of magnitude by questioning the mind of an intangible almighty...

It's very strange how, at the very moments when we need to invoke God the most, his existence always complicates the situation much more than it deconvolutes it, at least from a rational perspective...