When I first came to Japan many years ago the thing that struck me the most was seeing people wearing what I thought were surgical masks in public places. Before that I had only ever seen people wearing them on American TV programs set in hospitals, or during my one experience as an in-patient when my appendix burst just before my 18th birthday.
Why do they do it, I wondered?
One of my British friends explained it to me. Japanese people are group-minded and they always do what is best for the group. If they are ill, they don't want to spread their germs to other people so they wear masks out of consideration.