Google’s latest release of the new version of Android Oreo was found that the addition called “roll back protection (Rollback Protection)” new features, including a mechanism to verify the start, it will disable the device to roll back to an older version of the firmware. If you try to install an old version of the official image will cause the device to fail to start.
It sounds like a good idea, but you can take PC to compare, such as your PC upgrade from Windows 7 to Windows 10, but found that there are many problems after the upgrade, you want to reuse Windows 7, the results found that the operating system prohibits you Downgrade. Or do you try to install Linux? Google has prevented users from choosing the dispute again.