It's invisible to you until you actually realize it's (partly or fully) ineffective by getting sick. With a mask, you have some general idea well before you'd a

It's invisible to you until you actually realize it's (partly or fully) ineffective by getting sick. With a mask, you have some general idea well before you'd actually get sick. You can see if someone's wearing a mask properly, but you can't analyze their immune cells and the specific pathogen strains they might be exposed to.