Anyone whose shoe has worn thin enough for a nail to press through into the foot can have some sympathy for the sufferings constantly threatening the old Romans.
They were not troubled with nails coming through the soles of their sandals, but there was every likelihood of picking up a sharp pebble, and no stocking even to protect the tender foot.
The word for such a pebble or pointed bit of stone was scrupulus, from which our word scruple developed. It is easy to see how the uneasiness one would feel from a pebble in the sandal gave rise to the figurative use of scrupulus for an uneasiness of the mind.
The small apothecaries’ weight, scruple, came from the same Latin source.
And our adjective, scrupulous, which denotes extreme caution and carefulness, suggests the care that the old Romans would take in traversing a road described as scrupulosus, “full of tiny sharp pebbles.”