It's happened 21 times before. And it's become such a political attention seeking tool that they've written laws to remove almost all consequences to the American public from it. They've legislated away the entire point of shutting down the government to make it mostly theater and headlines. It's meant to sow hardship to the country, and motivate people to make changes to leadership. Instead, it's a clownshow for everyone to use for their 24/7 campaigning.
"We're going to SHUT IT DOWN!! (except Social Security, law enforcement, border security, millitary, health care and a bunch of other things that actually matter)! You wouldn't want us to SHUT DOWN THE GOVERNMENT (except Social Security, law enforcement, border security, millitary, health care and a bunch of other things that actually matter) would you? That would be bad if we SHUT DOWN THE GOVERNMENT (except Social Security, law enforcement, border security, millitary, health care and a bunch of other things that actually matter)"
What ends up actually happening is you can't go to the Grand Canyon for a few days because the National Parks system closes. Everything else is administrative and doesn't have an immediate impact on anyone.