Single Source of Truth

One system designated as the authoritative record for a given piece of data, so other systems reference it instead of holding their own conflicting copy.

Without a designated single source of truth, the same piece of information (a customer's current address, an item's stock level) can end up stored differently in multiple systems, and nobody can say confidently which one is correct. Establishing one authoritative source — with everything else referencing or syncing from it, rather than maintaining an independent copy — is what makes reporting and automation trustworthy.