Articles

Long-form writing on software engineering, systems design, and building things.

January 24, 2026

System Boundaries Become Visible Only When Crossed Incorrectly

Every system operates on assumptions. Some are explicit—enforced by types, schemas, and validation. But the dangerous ones are implicit: "events are ordered," "usernames are lowercase," "this array is sorted." These invisible boundaries work perfectly until someone crosses them. Then a service that ran flawlessly for months suddenly explodes on "valid" data. The bug isn't in your logic—it's in the gap between what your system claims to accept and what it actually handles. Good architecture closes this gap by making boundaries impossible to cross incorrectly, not just expensive to cross incorrectly.