"There are known knowns, ... there are known unknowns, ... but there are also unknown unknowns." Donald Rumsfeld's musings about terrorism are a good way to think about the COVID-19 pandemic right now. We know that masks are effective at reducing transmission. We know that the role of children is poorly understood, yet vitally important for planning a safe return to school and work. We do not know what long-term consequences of infection, even from "mild" cases, have not yet appeared. Case in point: https://www.nytimes.com/2020/08/17/opinion/covid-19-heart-disease.html #COVID19 #uncertainty