I remember this story a bit differently: he came across the nail clipper in the grass next to the shared trail in the DMZ and left it alone, since if he picked it up, the South Korean that lost it would accuse the North Korean border guards of theft of a valuable tool and spark a diplomatic incident.
The next few times he patrolled the trail he would check if the clipper was still there, and it was. What was more puzzling, the grass along the sides of the trail showed no traces of a search. Then he realized that no one was coming back for it, that not only was South Korea so rich that a random border guard could afford a nail clipper, but it was so much richer that the loss of a delicate tool like that was just a mild inconvenience, that the guard must've just went and bought another one.
The next few times he patrolled the trail he would check if the clipper was still there, and it was. What was more puzzling, the grass along the sides of the trail showed no traces of a search. Then he realized that no one was coming back for it, that not only was South Korea so rich that a random border guard could afford a nail clipper, but it was so much richer that the loss of a delicate tool like that was just a mild inconvenience, that the guard must've just went and bought another one.