In Hyun Hyun, the thong of a sandal snapping is bad luck. It comes from the tale of a nomadic trader – a struggling inventor traveling up the highway, which was full of the requisite highwaymen. He managed to avoid them until coming to a sheer precipice. There was no way down except the highway itself, but here a great robber lay in wait. As the inventor padded around in admiration at the view of ice floes, his sandal thong snapped. He stooped to fix it as the great robber sprang, and so flew over his head and down the precipice. Presumably he died. He never shows up in any other stories.
The inventor fled barefoot into the city beyond the highway, evading the great robber’s goons. Kindly sages sheltered him and foolishly cured his frostbite. He even retained enough of his wares to trade for the unique local materials, from which he crafted his most infamous product: gunpowder.