In Japan, if you cut off your nails at night you won’t be able to see your parents die. This doesn’t mean that you’re going to go blind. Not being able to see your parents means dying sooner than your parents. This superstition is pretty old and has roots back in the era where there was not enough lighting in the house so it was dangerous to use sharp objects in the dark. It’s believed that this superstition was created to decrease the possibility of danger.