Google has built a security feature into Android which will lock you out of your device if you Factory Reset your phone without first deleting your accounts from the device. The only way to get past the FRP lock out is to enter your Google account information. That is great if you are locked out of your device, but if you have sold your device or given it to someone else they may find themselves locked out of the device if they don't have your Google account information. This is mainly meant to be a security measurement to keep people from stealing Android phones and just being able to wipe them clean to use them as their own. There are ways to bypass this Factory Reset Protection. The only person dedicated and patient enough to find these bypass methods is RootJunky! He has just released his tedious method for bypassing the FRP on the new Pixel devices. The same method works for the Nexus 6P and the Nexus 5x. The video is 20 minutes, and this is not for the faint of heart!