Schneier - Mailbox Master Keys

Here's a physical-world example of why master keys are a bad idea. It's a video of two postal thieves using a master key to open apartment building mailboxes.

Changing the master key for physical mailboxes is a logistical nightmare, which is why this problem won't be fixed anytime soon.

from Schneier on Security https://www.schneier.com/blog/archives/2020/01/mailbox_master_.html