ppl are wearing masks while grocery shopping. But they take it off immediately after leaving grocery.
This is what I do. To me, it makes sense to wear a mask in situations with a high probability of transmission, and not in others. This is the result of a synthesis of information I've heard from Japanese experts and experts from other countries, namely the US.
Upthread, someone mentioned nose breathing, maintaining distance, and wearing a mask as combining for a 99% prevention rate, and that any two of them together is 95%. I take that to mean that any one of those precautions adds just 4% when viewed as the third measure.
Here in Japan, they're telling people to avoid the three Cs--closed/poorly ventilated spaces, crowded places, and close-contact settings--and that the situation is particularly dangerous when they overlap, which I take to mean "not as dangerous when you have satisfied all three or two of the three."
These days, the store is the only place where my wife and I, who have not had more than 15 seconds of face time at once with anyone but each other since mid-March, enter the three Cs, so I mask up at the store and take it off as soon as we're away from the crowded area.
On our twice-daily walks, which we have altered specifically to avoid crowds, none of the three Cs comes up, so I don't mask up. We can't maintain 2 m of distance where it isn't possible, but we pass or hang back of people going the same direction, stay in constant motion, and don't touch anyone or anything with our hands. I think that accomplishes enough, and makes the mask and its +4% not worth the trouble (heat/fogging up glasses, as these walks are brisk).
If not wearing a mask at all times in public (which I take to mean anywhere outside the front door) is selfish, as some on this thread have claimed, then I think I'm making reasonable choices as to when to be selfish (plenty of distance, very low risk of transmission).
