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In spite of what you would suppose, the facts are not reversible. Just because you are able to get in, that does not mean you will be able to get out. Entrances do not become exits, and there is nothing to guarantee that the door you walked through a moment ago will still be there when you turn around to look for it again. That is how it works in the city. Every time you think you know the answer to a question, you discover that the question makes no sense.

Extract from In the Country of Last Things, Paul Auster