When a business application misbehaves, the visible error is rarely the real cause. These six root causes explain the large majority of production faults we diagnose.
1. Unvalidated input and edge cases
Systems built for the happy path break on real data: unexpected characters, huge files, duplicate submissions, expired sessions mid-form. Fix: validate everywhere, handle edges explicitly.
2. Permission logic drift
Roles added over years without review. Users see too much, too little, or actions fail with cryptic errors. Fix: audit roles against actual jobs, test every role.
3. Integration brittleness
Hard-coded assumptions about vendor responses that break when vendors change anything. Fix: defensive parsing, retries, visible failure queues.
4. Data-quality decay
Duplicates, orphans and legacy inconsistencies that break new features. Fix: constraints, cleaning and validation at the source.
5. Dependency rot
Years-old libraries with bugs fixed upstream long ago. Fix: update cadence with regression testing.
6. No error visibility
The meta-cause: faults occur for weeks before anyone notices because logging and monitoring were never set up. Fix: structured logging, alerts and a weekly error review.