The single source of truth, explained
When the same fact lives in five places, all five eventually disagree. A single source of truth is the cure for a whole class of problems.
A customer's address is in the CRM, the billing system, the shipping tool, and a spreadsheet. They were all correct once. Now they disagree, and nobody knows which is right. This is the problem a single source of truth solves.
Copies drift
The moment a fact is copied, the copies start drifting apart. One gets updated, the others don't. Over time you accumulate contradictory versions and spend real effort reconciling them — or worse, acting on the wrong one.
One home, many windows
The fix isn't fewer tools — it's deciding which system owns each fact, and having every other tool read from it rather than keep its own copy. The data lives in one place; everything else is a window onto it. Update once, correct everywhere.
If a fact lives in five systems, you don't have five backups. You have five future arguments.