Optimistic updates predict success rather than confirm it

An immediately updated counter shows a prediction, not proof that the server accepted the action.

Relay writes optimistic data before receiving a response, allowing selected components to display anticipated changes immediately.

The mutation guide documents rollback on failure and replacement with server data after success.

Concurrent optimistic changes deserve special care when their predicted values depend on previously observed store values.

A later prediction can preserve an incorrect count after an earlier operation fails and rolls back.

If Normalized caches need deliberate update policies, optimistic reconciliation must respect shared records and overlapping operations.

Because Colocated fragments make component data dependencies explicit, changing fragment selections also changes the optimistic payload contract.

Use immediate feedback only with visible failure handling and tests covering overlapping actions and rollback.