I've noticed in some of my fiction (particularly my short stories) I don't explain everything. I'm not talking about spoon-feeding a potential audience every little bit of info; more having characters in strange or uncomfortable situations and their efforts to get out of it or simply survive rather than saying why the situation has occured.
So if you read a book that leaves questions unanswered, are you OK with it or do you want total closure after the last page?
Again, the standard answer: it depends.
Does the lack of information hinder the story in any way? Do the readers need to know? How much info do you need -- are you going to have a full back story?
I think eventually people will want to know how they got there in the first place -- think of a show like
Lost. It's wonderful and suspenseful to put the character
in media res and not explain everything, but eventually, your readers will demand to know. The more mysterious the origin of the situation, the more they would eventually want to know the answer (another example comes to mind: The X-Files).
Now, it doesn't mean everything has to be explained. If the people are trying to escape a fire... I think it's okay if you don't explain how the fire got started. Like life, a lot of things don't have to be explained. It just is. As long as not knowing the info doesn't affect the story, I think it's fine. But if the background of the situation is important, then I think the readers deserve the answer. But you still have to decide what kind of details you need for your story. For example, in the movie
Sunshine, we need to know why the astronauts are going to the Sun... but we don't need to know how they each individually got selected and they back story and all that -- they may be relevant to the characters, but they are not relevant to the story -- but the back story of Icarus I (the previous ship sent to the Sun) is important because it's the integral part of the story, so we need to eventually know what happened.