What common mistake do developers make with Before middleware logic, why does the mistake cause problems, and what is the safer approach?

What common mistake do developers make with Before middleware logic, why does the mistake cause problems, and what is the safer approach? One recurring problem with before middleware logic is applying it without understanding the boundary it protects. Putting business-domain calculations into middleware just because middleware runs on every request. In addition, Middleware can inspect an incoming request and decide whether it should continue to the next application layer. 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.