Hey, I've got a good idea, why don't we prevent the spread of flu by all remaining in our homes and keeping them sterile at all times? Oh, I remember - it's because we are SOCIAL people who rely on communication and interacting with others to keep us sane. As Kyle points out, we don't generally wear masks, because the payoff (a slightly reduced chance of catching flu) isn't worth the cost (hugely reduced communication). Hence why a very effective punishment in our society is "solitary confinement", seeing nobody. Even in our playgrounds, if kids want to really upset someone, there are two ways of doing it - one is to physically or verbally pummel them, the other way is to ignore them completely, not speak to them, not look at them directly, cut yourself off from them. It used to be called "being sent to Coventry". Is it any wonder then, that we don't understand the people who WANT to cut themselves off, to not be recognised or spoken to by non-family-members?