This is an Indian story, and it goes like this:
There was a man travelling in a slow, crowded train on a hot day. The train was packed with people and every door and window were open to provide a bit of air. A sudden jerk made the man's sandal fall off, and the draft took it away through the open door.
The man looked for a moment behind his sandal, as if saying goodbye to it, then took his other sandal and threw it out.
"Why did you do that?" a man standing next to him asked.
"There's no use in having just one sandal. But if someone finds the one that flew away, he might also find the other one."