I still don't understand, and maybe this has changed since a few years ago, but how you can essentially brick a phone by re-locking the bootloader with a corrup

I still don't understand, and maybe this has changed since a few years ago, but how you can essentially brick a phone by re-locking the bootloader with a corrupt OS since unlocking the bootloader requires you to have access to it. I thought back when I did this that there would be a boot sequence I could put the phone into but that wasn't the case. Had to ship it in for service.