Before the first person died, there was already a library. No one had put it there; it had assembled itself from the probability of lives. The shelves came first; the books filled themselves in as people were born and began making choices.
There was a keeper, though she had not asked to be one. She had arrived by accident, following a path through the forest; she had found the door open and walked in, and when she tried to leave she found she preferred not to. This was common. The library did not trap anyone. It simply made staying more interesting than leaving.
The first visitors came from the nearest village, having heard that such a place existed. They came with questions: did the library show the future? The keeper said no, only the present, and every present that might have been. Was it allowed to copy down what one found there? The keeper said no. Could a person visit more than once? The keeper said yes, but most people only needed to come once, and the library had a way of showing you what you were ready to see, which meant second visits were rarely as useful as the first.
One man came back seven times before he understood that the book he kept returning to was not the point. The point was the shelf, the particular shape of his possibilities, which he had mistaken for a prison when it was actually a description of what he was made of.
The keeper did not have a shelf of her own. This had seemed unfair, until you considered that she had never needed one. She already knew what she was.
The library still stands in the same place. The door is still open. The keeper's position has not been vacated, though the keeper herself has changed many times, each one arriving by accident, each one deciding to stay. This is not a coincidence. It is a qualification.