I expected to Google this and be like, come on, really?
But this is interesting. It’s a few results down and you have to really refine your search to get beyond offline/download issues. Check this out.
Apparently if you use a Windows Online account with Outlook or one of their other services, your password with that service and the password on your Win 8/10 PC can get out of sync and LOCK YOU THE FUCK OUT.
EDIT: This is the search that got me there.
Way to ask the right question.