matter. People aren't going to stay home when they feel fine. They aren't going to keep their children home when they seem fine. That allows it to spread to others who are actually fine. Most of all of these people will have mild symptoms and recover. But in the meantime they're passing it to people who might not recover. There's also a vaccine for the flu which helps limit the number of cases and deaths which is not something we have for this virus. Again I don't think we're looking at a Black Death here or something. It's more subtle than that. I do think the possibility exists for the majority (50%+) of the people in the world to become infected at some point. And even if 99% of those cases are mild that would still be a ton of deaths and a major disruption to the world economy.