The first chart shows why events are being cancelled. We are at, or soon will be at, 10,000 infected persons, most of whom will not be showing symptoms. That means a random gathering of 300 Americans will have a 1% chance of having an infected person present, spreading the disease. With larger groups, the percentage will increase. With more people exposed in coming days, the percentage will increase.

The second chart shows that we must flatten curve to spare our health care infrastructure from being overwhelmed. This is the reason the event cancellations and travel bans on China and now Europe are key. The virus will get here, but the flatter the curve on the graph (the slower it gets here), the better chance our healthcare system will have of giving all of us good and appropriate care.