(Addendum: there’s the obvious question, why not just wear a mask 100% of the time? There are no downsides, right? — There can be. Perhaps my mask had been in use for a while, I suspect it’s gotten dirty enough to be a potential health hazard, but I don’t have another mask to replace it? I’d still use it if people are around, but would try to reduce my exposure to it otherwise. Maybe I have asthma or some type of breathing difficulty, and wearing a mask makes it worse? I think those two are probably among the most common reasons.)