What common mistake do developers make with Consistent errors, why does the mistake cause problems, and what is the safer approach?

What common mistake do developers make with Consistent errors, why does the mistake cause problems, and what is the safer approach? One recurring problem with consistent errors is applying it without understanding the boundary it protects. Returning HTML error pages from a JSON API without considering content negotiation and client expectations. In addition, A stable JSON error structure helps frontend and mobile clients handle failures predictably. 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.