Even though no 100% effective precautions or measures exist, it make sense to wear a mask, etc.: 1) To reduce the viral load on your immune system. Maybe not to zero, but very low. If low enough, the immune system might contain the infection with no symptoms or further transmission. 2) To attempt to delay infection until a vaccine and/or antiviral is available or the virus mutates to non-viable status and disappears.
Similar arguments can be made for use of supplements such as NAC and monolaurin.
To take no precautionary action whatsoever is not rational.
As an aside, I received my order of Ambroxol/Mucosolvan from the Ukraine. This appears to be a highly effective non-narcotic cough syrup available just about everywhere in the world except the Americas! Dumb!!! (Apparently never submitted to the FDA for approval). Also used in the treatment of respiratory diseases associated with viscid or excessive mucus, with potential application to CoV.