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

What common mistake do developers make with Public urls, why does the mistake cause problems, and what is the safer approach? One recurring problem with public URLs is applying it without understanding the boundary it protects. Saving user uploads directly under a public web directory without validating file type, name and access requirements. In addition, Publicly accessible files need an appropriate disk and URL strategy rather than exposing internal paths directly. 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.