Don’t follow it.
An unwritten rule by its definition cannot compel compliance. Only written rules can compel compliance, hence a cop may give you a ticket only for violating the written rules.
The unwritten rule’s power is found in your willingness to submit to it and your fear of the consequences if you don’t.
If you refuse to submit, then it stops being powerful.
If you resolve yourself to live up to the consequences, then you’ve conquered it.
I hypothesize that if the rule mattered so much to the effective workings of your organization then someone would have written it down by now.
Unwritten rules are the controls through which powerful organizational figures wield power that they dare not claim officially (via written rules).
Unwritten rules are the way leaders maintain excuses for not walking their own talk.
Unwritten rules are the way employees make themselves accomplices in organizational decline while preserving their victim status at the same time.
You can do better.
My suggestion: find an unwritten rule that’s hurting you or your organization and try to kill it.
Let’s see what happens.
[WARNING: Killing unwritten rules may indeed bring unwritten negative consequences (e.g., unhappy looks, counseling sessions, loss of holiday party invitations and more). Kill at your own risk.]