Thought experiment: Take a small sip of beet juice and then simulate a sneeze or a cough while standing several feet in front of your clean white wall. Next, take another sip, wrap a handkerchief around your face and then sneeze / cough / spit. See how far that "virus juice" flies when you wear a mask?

If everyone wore a mask, then all the people who are sick are effectively increasing their social distance from the healthy people. Even if the sick person walks within 6 feet of you, their effective social distance might be greater than 6 feet if they are wearing a bandana, t-shirt, surgical mask, etc.

Wearing a face mask works on a population scale. Everyone should be wearing a mask.