The words "fall" and "lie" can, of course, be connected to the collapse of the World Trade Center's towers. "Fall" can also be symbolic of Oskar's life as he finds himself in a mental free fall, trying to make sense of the inexplicable and unravel the "lies" that various people (he perceives) are telling him to keep him from the truth (burying an empty coffin, for example.)
Finding a "reason for being" is at the heart of the existential crisis of Johnathan Safan Foer's novel: “Just because you're an atheist, that doesn't mean you wouldn't love for things to have reasons for why they are.”
People want to make meaning of events. Religious people can say it is "God's will," even if that is often not a very satisfying answer. For those without a religious system of belief, the inability to connect action to reason is frustrating, to say the least.