What are some potential reasons for files not being uploaded successfully in PHP?

Some potential reasons for files not being uploaded successfully in PHP could be due to incorrect file permissions, exceeding the upload_max_filesize or post_max_size limits in php.ini, or missing enctype="multipart/form-data" attribute in the form tag. To solve this issue, ensure that the file permissions are set correctly, adjust the upload_max_filesize and post_max_size limits in php.ini if needed, and include the enctype="multipart/form-data" attribute in the HTML form tag.

<form action="upload.php" method="post" enctype="multipart/form-data">
    <input type="file" name="file">
    <input type="submit" value="Upload File">
</form>