The most dangerous lie in tier-0 migrations is not “this will be quick.” It is “we can always roll back.”
That sentence sounds reasonable when you are migrating a stateless service or swapping a cache. It becomes fiction when the system you are retiring holds years of operational history, audit-critical records, dispute workflows, and the kind of long-tail queries that only show up when something goes wrong at the worst possible time. In 2026, the pressure is higher because data retention horizons keep stretching while reliability expectations keep tightening. You are not migrating a database. You are migrating accountability.