What are common pitfalls to avoid when using include functions in PHP to avoid "failed to open stream" errors?

When using include functions in PHP, common pitfalls to avoid to prevent "failed to open stream" errors include providing the correct file path, using the correct file extension, and ensuring file permissions are set correctly. To avoid these errors, it is important to specify the correct file path relative to the current file location and to use the correct file extension (.php). Additionally, make sure that the file being included has the appropriate read permissions set.

<?php
include 'path/to/file.php';
?>