The CAP Theorem, Consistency Models, and the Trade-Offs Nobody Warns You About
Every distributed system I have built forced a conversation about consistency before it forced a conversation about performance. Sometimes that conversation happened during design. More often it happened at 3 AM when a customer reported stale data, a checkout double-charged, or a dashboard showed a record that had been deleted twenty seconds earlier. The CAP theorem gets referenced in every system design interview and every architecture document, yet most teams still get caught off guard by what it actually means in production. The theorem itself is simple. Living with its consequences is where the engineering happens.