You have no idea...
I worked for a small gov agency, our finance was done by a bigger related, agency. They, in their infinite wisdom, decided to upgrade, the hardware, the operating system version, the database version and the application for their finance division in one hit over a weekend. A consultant vaguely attached to the project told me he was taking some time off and going far, far away whilst it happened. Needless to say it didn’t go well. I’ll admit it was the late 90s but even so I was horrified. We ended up running dept finances on separate spreadsheets, with a master spreadsheet pulling everything together for finance so that they had some sort of accurate picture for our parent ministry, for a year! The team I was in got lauded for coming up with a fix for ourselves, the other team…well government! Unless you’ve worked there you have no idea