Do you have a WordPress site? Do you keep it update?
What happens when you use the automatic updater and the update craps out on your for one reason or another? Nothing, often. You can still go about your business and try again.
But, of the upgrade has begun, WordPress puts your site in Maintenance Mode and you can’t access any part of it until that state goes away.
This is frustrating. So, what can you do?
You should be able to get into your site again.