For two decades, we've accepted a compromise. We put all our customers' data in one database. We added a tenant_id column. We wrote WHERE tenant_id = ? a thousand times. We called it "multi-tenant architecture."

We told ourselves it was fine. It's not fine.

One query without a WHERE clause = data breach.

One heavy customer = everyone slows down.

One compliance audit = "show me the isolation."

One mistake = trust destroyed.

• We wouldn't share bank accounts with strangers.

• We wouldn't share house keys with neighbors.

• We wouldn't share passwords with coworkers.

  
  

Why do we share databases with other companies' data?