Needed to look up some info in Contacts. Open the app and saw that there were absolutely zero entries!
Since I had only recently "upgraded" to Catalina, I assumed this was just another "minor" problem. I've just spent half an hour searching for various terms, running Find Any File on all drives, searching TM volumes and dozens of sites around the web. All that time was simply wasted.
I finally reopened Contacts and looked at it's prefs. Contacts->Prefs->Accounts: "Enable this account". That checkbox was UN-checked.
Clicked that box and saw the Contacts miraculously re-appear in the app. Why does Apple do these things? Why does that fact show in any searches I made?
Other self: "
Don't I often hear you telling people to always check the prefs for any apps they install?"
Self: "
Well sure, but I didn't "install" Contacts, Apple did!"
Other self: "
Sure, but you decided to install Catalina... Accept the blame and move on!"