... Therefore, the "safest" assumption is to operate as if everyone is contagious/sick and apply standard precautions universally. When we operate under the assumption that everyone is contagious then the scenario changes and wearing a facial barrier makes far more sense.
The logic of self isolation and social distance is simple:
If one in 100 people are infected, the chance of you getting the virus from someone you meet is 1/100. If you meet another it has doubled, another and it has tripled ... every person you meet increases the chances that you will get infected.
Social distancing increases the path the virus must travel to infect you. If the virus spreads from a person as they exhale it will be an expanding cloud of the exhalation with a finite number particles of virus, the density of particles therefore drops with the distance from the center of this cloud as it expands, ie -- the chances of you getting in contact with a virus lessens substantially the further you are from said person.
Stay safe, minimize contacts with others, wear a mask outside the house, and keep a respectable distance from others.
Enjoy