Duplicate a fact for convenience and you've scheduled a future disagreement.
I'd copied the same fact into a few places because it was handy at the time. Then they drifted, and I couldn't tell which copy was true. The discipline that fixed it: a storage-ownership model — every kind of fact has exactly one home, and everything else points at it.
I tested mapping where each kind of information is allowed to live and running an audit that flags the same fact showing up in two homes.
One fact, one home. No copy to drift, nothing to reconcile, no 'which one is right.'
Convenience-duplicating. Every copy is a fork waiting to disagree.
One fact, one home. The second copy isn't a backup — it's a future bug.