Epic fail because there isn't an option to select another account for the login screen. The switch user account option is disabled in that only one user can login at a time.
So with the system not login out the previous user, the system is locked to the user account that is logged in with no option to log another user account in (including the admin user). So yes Epic fail.
Can't believe there's isn't a way to force sign out someone.
How is this an "epic fail"?
When you start your computer (assuming you are using your Microsoft Account) the screen will offer you a choice of sign in options (accounts) and you sign in with your own account info and password/pin/whatever.
Yes, that will sign out anyone else who may have been logged on previously and they would (possibly) lose unsaved work. But, unless they are unbelievably thick they would have saved their work before shutting down the computer anyway so, really, any such risk is negligible.
The same is true for local accounts. Just go ahead and sign in with YOUR password and account info.
And when you're ready to sign out say "Hey, Cortana, sign out."
You can also tell her to shut your device off or lock it if you're going to be away for a bit.