How can developers troubleshoot file inclusion issues in PHP projects effectively?

File inclusion issues in PHP projects can be effectively troubleshooted by ensuring that file paths are correctly specified and that the included files exist in the specified location. Developers should also avoid using user input directly in file inclusion functions to prevent security vulnerabilities like directory traversal attacks. Additionally, using absolute file paths instead of relative paths can help in resolving file inclusion problems.

// Example of using absolute file paths to include files securely
include_once(__DIR__ . '/path/to/file.php');