It comes from seropositivity rates in blood samples. it comes from wastewater tracking for covid. It comes from everyone you know having had it (suspected or confirmed). It comes from public health experts saying only 1 in 10 cases has been recorded and comparing that to caseloads over the course of the pandemic. It comes from the fact that the disease is even moving back and forth between people and animals that's how common it is. Bats to humans, humans to deer, rats a cause of variants, humans to felines, etc. It's here and it's not going away. With animal reservoirs even if we welded shut the doors of every positive person like they do in China it will never go away.