“When you build a new house, make a parapet on your roof” (Deut. 22:8), i.e. make sure that whatever you do does not expose you or anyone else to risk. If you build a house with a flat roof, make sure no-one will fall off the edge.
The parapet, said the sages, had to be at least two cubits high. It might disturb the architectural beauty of the building, but it would save life. Similarly, any negligence on our part which might endanger a person must be protected against.
The Hebrew for parapet is ma’akeh, and some suggest that it may be reconstituted as the initials of four other words – Hirhurei Averah Kashim Me’avodah, “Sinful thoughts are harder (to control) than the sin itself”.
Everyone therefore needs a notional parapet around themselves to ensure that careless thoughts do not lead to a fall into sinfulness.