There was a city with one train station, and for as long as anyone could remember everyone had boarded the same train. It had many cars — first class, third class, a bar car where people fought about the destination — but it was one train, and it went one way, and when it arrived everyone arrived together. Then, one autumn, the stationmaster posted a new timetable. There would be many trains now. Same station, same hour. Tracks that began side by side and, somewhere past the city limits, bent apart. Nobody read the notice. It was a strange autumn. Everyone was busy.

The station's old clerk kept a prism on his desk, and when the trains began to multiply he pointed at it more than he spoke. Sun came through the window as one beam and left the glass as a fan of colours, each one whole, each one going somewhere different. 'That's what's happening,' he'd say. 'Not a war. A prism. You are all one light and you're leaving as colours. Red isn't wrong about blue. Red just isn't blue anymore.' The travellers nodded politely and went back to arguing about which colour the light really was.

On the platform something odd began. People who had talked every day found that their words weren't landing. They could see each other perfectly — every gesture, every expression. But when one spoke, the sentence seemed to hit something clear and hard and bounce back into the speaker's own ears. Not silence — echo. A woman said 'Can't you see what's happening?' and heard only herself, asking. The man across from her said the same words and heard only himself. Both went home certain the other had gone deaf. Neither had. There was glass now, where there had been air.

The clerk was asked how anyone could tell the split was real and not just a bad year. 'Simple,' he said. 'Watch for two people who both sincerely believe what they're saying, and what they're saying can't both be so. Not liars. Honest people. That's the first symptom. You are no longer hearing two opinions about one world. You're hearing two reports from two worlds, delivered on one platform.' The travellers thought about the arguments at their own dinner tables and grew quiet, because they had already seen it, and hadn't had a name for it.

Out past the city limits the tracks were only a stride apart, and for a season people hopped between trains as easily as changing seats. A man boarded the train of anger, rode it for a week, and stepped across to something gentler when he'd had enough. That was allowed. The clerk was careful about this: 'While they're close, you can change your mind. Nothing is decided by a bad day. But they don't stay close. Every mile they widen. What was a step becomes a jump becomes a gap you'd need a bridge to cross.' The man made sure, from then on, to notice what train he was on before it got far.

A traveller spent a year pressed against the glass, shouting to the people on the other track — proof, articles, pleading. Nothing landed. He grew hoarse, and bitter, and his own train slowed under the weight of him. One day the clerk sat down beside him. 'They can't hear you. Not because they're stupid. Because the glass is real. You're not failing to reach them. You're succeeding at reaching yourself, over and over, with your own worst voice.' 'Then what do I do?' 'Ride your train. Ride it well. That's the only thing that's ever visible through the glass.'

The year the trains multiplied had a number that meant clear sight, and the clerk liked that. 'Look back,' he said, 'and see, clearly, what you've been choosing all this time without calling it a choice. Then look forward, and choose clearly what you prefer.' Not what's right. Preference. It sounded too small to matter. But a woman on the platform tried it — sat down, looked backward at ten years of boarding whatever train was loudest, and forward at the one she actually wanted — and found that the wanting alone had moved her three tracks over without her standing up.

Some travellers were frightened by the sound the station made now — a creaking, as if the old building couldn't hold. 'It can't,' the clerk agreed. 'That's not the building failing. That's the building being outgrown. Every seam that splits is a place the next thing gets in. The old way was: when it can't hold, tear it down and start over. The new way is: when it can't hold, step sideways into the version that already fits, and let the old one fall off you like a coat.' The creaking didn't stop. But it sounded different, after that. Like something being born rather than something breaking.

The tracks kept widening. One morning a traveller looked across for the train of the people she used to argue with and couldn't find it. Not gone — too far. Beyond the curve. She waited for the grief and it didn't come. She had chosen her train and ridden it well, and they had chosen theirs, and each was now in a world that matched, and the worlds no longer touched. 'That's not loss,' the clerk said, when she asked. 'That's arrival. You'll live in the world you prefer. So will they. Both are real. You were never going to make one world out of two preferences.'

At the very end of the platform the clerk kept one sign, and it was the only one anyone needed. It didn't say which train was correct. It didn't rank the colours. It asked a single thing, and asked it of everyone equally: what do you prefer? Not what is right, not what will win, not what the loud car says. What is actually yours — what lifts, what feels like truth and soul and the shape of your own life. Answer that, and you're on your train. Answer it again tomorrow. That's the whole timetable. The glass was never the enemy. It was just a way of letting everyone go home.