When a validation failure causes a redirect loop
Laravel’s default behavior on a failed FormRequest validation is to throw a ValidationException, which the framework’s exception handler converts into a redirect to the previous URL with the input flashed to the session and errors attached.
That works perfectly when a person submits the form as the redirect lands them back on that page with the errors.
It breaks down when the form submits itself, for example a bookmark to a GET form with validation, or submitting something into a target="_blank" (like PDF generation).