I followed the New Zealand press conferences very closely and so often the initial story was this person had no symptoms, total surprise to them that they had the virus, and then a day later oh, well, actually they did have some symptoms but they didn't realise it was COVID-19...

People will say to themselves well, it's just a cough right? Just a cough. I can't have COVID-19 that's something other people get, those people are sick but I'm healthy, this is just a cough. And that allows the virus to spread.