COVID-19 Check-in Thread Part II

[hazard]

Sure, one person going out and seeing all his friends won't do that much harm.

The problem is all his friends, because they are also one person going out to see all his friends, and most groups of friends have overlap between individual members' groups of friends, but those overlaps are rarely completely the same.

Which means you don't get one person going out to see 1 group of friends. You get thousands of people all seeing thousands of groups of friends between them, with much overlap in total but not on the small, individual scale.

And that's how you spread a contagious disease.