One of my colleagues tried upgrading his Windows 7 laptop to Windows 10... he had multiple issues getting the installer to run but got past it after a couple of hours troubleshooting.

He left for lunch when it got to 81% installed, and got back an hour later to find "Something Happened" proudly displaying on-screen.

He clicked 'okay' and it just started rolling back to Windows 7 with no explanation as to what happened, or even any error codes!

Thanks Windows!
As helpful as always!