Wearing a mask helps to protect OTHERS and YOURSELF. If the person you are interacting with and you both wear a mask, much more protection. If only one wears the mask, the person without the mask is more apt to lean in closer. People have also been known to accidentally spit when they talk and if they are unknowingly in the contagious stage, their mask would contain their saliva. Without the mask, the airborne saliva is now on you or you inhaled particles without your awareness. If neither person wears a mask, someone has inhaled and now both may be contagious with either person knowing.