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Feature flags reduce deployment risk, but over time they can quietly reshape system behavior in ways that make correctness harder to reason about.

Tests often pass while production still fails because the system assumptions encoded in the suite are narrower than the conditions production actually creates.

Some bugs surface only under real traffic because production load changes timing, concurrency, and failure behavior even when code paths look identical.

Adding an index often seems like the obvious SQL fix, but query latency can remain unchanged when the planner and data shape disagree.

Caching can improve performance, but it often makes system behavior harder to reason about through stale data, invalidation drift, and timing issues.