What common mistake do developers make with Measuring query cost, why does the mistake cause problems, and what is the safer approach?

What common mistake do developers make with Measuring query cost, why does the mistake cause problems, and what is the safer approach? One recurring problem with measuring query cost is applying it without understanding the boundary it protects. Adding eager loading everywhere without considering payload size; loading ten large relationships can be as problematic as under-loading. In addition, Query logs, application profiling and realistic data volumes are useful when verifying whether relationship loading is efficient. Safer engineering approach: keep the responsibility in the correct layer, use the framework's supported API, validate and authorize inputs, avoid hidden side effects, and verify the behavior with tests.