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

What common mistake do developers make with Request validation, why does the mistake cause problems, and what is the safer approach? One recurring problem with request validation is applying it without understanding the boundary it protects. Putting database queries, validation, notifications and complex business rules into one very large controller method. In addition, Controllers often trigger validation directly or receive validated data from Form Request classes. 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.