Least Privilege

Give every part of the system the smallest set of permissions it needs to do its job, and no more.

How to use it. Start with no permissions. Add what is needed. Audit what is granted. Most production breaches are made worse by accounts and services that had powers they did not need.

How it gets misused. Applied at setup and never revisited. Permissions accrete. The system you run today probably has accounts with powers nobody remembers granting and nobody dares to remove.