COVID-19 is a smart disease, it comes off as a mild disease at first but it can still spread easily. You can even spread it without feeling symptoms yourself. If a person feels too ill to not be moving around, it would already have passed the virus down to many contacts.
Social distancing is therefore vital when patients keep coming out of nowhere. If there's a group of people they could easily spread the virus before they even know. If people don't listen, it may have to be enforced for public safety. It's the approach China, Singapore, and South Korea have done and succeeded in various levels.
Because the individual makes the wrong call for the whole.